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is the Journal of the Biological Society, Victoria University of Wellington, New Zealand, and is published three times a year, with the financial assistance of the University Publications fund.
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Bats have a remarkably extensive distribution, even occurring on many remote oceanic islands. Flying foxes and blossom bats are found in tropical and subtropical zones from Africa to Australia and Polynesia. Some flying foxes measure five feet across the wings. These large bats comprise the suborder Megachiroptera, and with few exceptions have claws on both the thumb and index finger. The blossom bats have extremely long delicate tongues which they extend into flowers for nectar and pollen. They pollinate several tropical plants. Flying foxes congregate in roosting areas or ‘camps’ during the day and feed on fruit at night. Only the thumb is clawed in the small bats of the cosmopolitan suborder Microchiroptera. Generally insectivorous, this group includes also the true vampires, or blood-seeking bats, small tailless animals which, contrary to superstitious belief, are found only in tropical America.
Most bats of temperate zones hibernate during the winter months. They may be solitary, roosting beneath the bark of trees or at the sides of birds’ nests, or they may congregate in their hundreds or thousands in caves, hollow trees or disused buildings. Their hands modified to form large wings no longer serve for grasping, and most bats roost upside-down, clinging to rock walls or tree branches by the strong recurved claws of their toes. To many people bats are repugnant. Cold to touch and apparently stiff and moribund by day, these creatures take to the wing at dusk. Their remarkably silent flight is characteristic and it is little wonder that bats are held in superstitious fear. Even to the early Maoris the small ‘pekapeka’ foretold of death and disaster.
Two small bats, of the size of a mouse, are New Zealand's only known native land mammals. The few reports of the existence of a third species have not yet been confirmed. There are, however, instances of Australian bats being found here, but these are considered to be accidental wind-blown migrants. Both New Zealand bats are bush-dwelling animals usually seen only during twilight as they pursue insects over clearings or rivers and lakes. Fine summer and autumn evenings are favourable for observing these secretive animals.
Their rapid erratic flight makes observation on the wing difficult and identification to species virtually impossible. If captured, the species may be immediately distinguished by the length of the tail. In one, the long-tailed bat, the tail is almost as long as the head and the body, and is contained for its entire length in an interfemoral membrane stretched between the legs. The other bat has a short free tail above, but not
This short-tailed bat. Mystacina tuberculata Gray, is peculiar to New Zealand, and Dobson's suggestion that it was unique in being the most active climber of all bats appears to be substantiated by recent observations. Its agility is facilitated by the remarkable manner in which the wings may be folded. For this and other reasons its relationships are obscure and it is considered the sole representative of a family, Mystacinidae. In Chiroptera only the rare Myzopoda aurita of Madagascar shares comparable family status by itself. Some similarities are apparent between these two animals but at present our bat is considered most comparable with the widespread tropical group of free-tailed bats referred to as the family Molossidae.
Chalinolobus tuberculatus Forster, the long-tailed bat, is one of six species of the Australasian genus Chalinolobus. This group of lobe-lipped bats is most nearly related to South Africa's Glauconycteris and is included in the cosmopolitan family Vespertilionidae. The New Zealand Chalinolobus is closely similar to C. neocaledonicus of New Caledonia and C. picatus of northern and eastern Australia.
Knowledge of New Zealand bats dates from Cook's second voyage to this country during the late eighteenth century when Forster captured a long-tailed bat in Queen Charlotte Sound. Considerable confusion resulted from Dr. Gray's subsequent identification of short-tailed bats with Forster's animal. The New Zealand Chalinolobus was later synonymised with an Australian species, C. morio Gray. Past accounts of these animals are therefore difficult to correlate with the species as now known. This is particularly true of C. tuberculatus. Tomes' description, which alone is based with certainty upon New Zealand material, does not mention the characteristic lip-lobule and misses several other notable features. Because of these omissions from his description, the specific status of this New Zealand bat was not recognised. The structures themselves would have been indistinguishable in poorly preserved specimens.
Both species were formerly present over a greater part of New Zealand than now. Even at the beginning of the century they were still to be seen on occasion in some of the main urban areas. They were particularly recorded as roosting in large numbers under the bridges of the river Avon in Christchurch, but they have apparently failed to urbanise.
The map gives the broad picture of the present known distribution. It is based upon observations for the past thirty years. It shows also localities at which specific identification has been made. In the North Island colonies are still being reported from the upper reaches of the Wanganui River and from the area including the Rotorua and Waikaremoana districts. In the South Island more sightings are recorded for north-western Marlborough, Nelson and northern Westland than for other areas of comparable extent. Although few records exist it is possible that bats are present in Fiordland.
showing
Distribution of Bats
Of the islands adjacent to New Zealand, Little Barrier and Kapiti in the north and Stewart Island and its subsidiary islets in the south still support numbers of bats. Of these the southern islands have a considerable population of Mystacina but Chalinolobus has not been positively reported from them. The southern Mystacina are remarkably robust and differ in several other respects from their more delicate northern relations sufficiently to suggest a distinct subspecies. Data are as yet insufficient to determine the northern limit of this larger subspecies.
Our bats are nocturnal and generally insectivorous. Chalinolobus emerges in the early evening from late spring to autumn, and while occasionally seen on damp cloudy evenings it is more frequently reported on the fine warm nights of late summer and early autumn months. Flight is quick, soft and noiseless, and characterised by many rapid changes of direction. Group flighting is usual and regular feeding areas may be established; these changing only slightly from year to year. The numerous observations of C. tuberculatus over areas of water suggest that mayflies and mosquitoes form a substantial part of this bat's diet. The remains of these insects are found in bat droppings. Small moths and larger insects are sometimes taken and the rapid jaw action quickly reduces such items to a pulp.
Mystacina appears later, after dusk. On Stewart Island it has been found most active from 10 p.m. to midnight, but in the Rotorua district observations show that during the late summer it probably leaves its roost about 8 p.m. This two-hour interval would appear to correlate with the difference between the twilight times for the two areas. During summer this difference is of the order of two hours.
Mystacina pursues insects on the wing, flying at times close to the ground. It may come into the vicinity of lights and has sometimes stunned itself against torches and lanterns. In captivity Mystacina readily accepts food from the floor of the cage, and this together with its ability to run quite rapidly and its adeptness when climbing suggest that it may capture much of its food on the branches and leaves of trees. Food includes fairly large insects; spiders, crickets and moths being quickly accepted. Strong transverse ridges on the tongue of this bat are suitable for scraping flesh from animal carcasses and Mystacina has at times caused considerable damage to the bodies of mutton birds when these were hung to dry. It has not yet been determined whether this bat behaves as a natural scavenger.
Both New Zealand bats congregate in some numbers during the day although occasionally one or a pair of bats may be found beneath the bark of trees such as that of Kahikatea. The roosts occur in the hollow branches and trunks of large forest trees or in caves if these are near bush. A single roost may be inhabited for long periods and great accumulations of droppings are sometimes found. Such roosts are characterised by a strong musty smell.
A roost of Mystacina usually contains seven to ten individuals of both sexes. A favoured hollow can be deserted for a week or more before being reoccupied. C. tuberculatus may form colonies of many hundreds but even such numbers as these are small in comparison with those of species elsewhere.
During the day the body temperature of bats drops. If disturbed at this time they are extremely sluggish and require a period of warming up before becoming active. This process involves yawning and stretching and disturbed bats may produce a shrill squeak. Of our bats only C. tuberculatus undergoes true hibernation.
The roosting habits permit ready transfer of ectoparasites between individuals and the fur of bats is usually infested. A relatively large bat flea is known from both our species. Mystacina is frequently host to numerous small mites.
Moreporks are the only native predators of bats and the wings of bats are sometimes found in their nests. Bats have been seen to escape an attack by flight in a fast upward spiral. Rats and the introduced mustelids are suspected in some localities of preying on at least Mystacina, and while records exist of capture by cats and dogs these latter animals would play but little part in reducing the numbers of our bats.
There has been a decrease in the distribution of native bats which is correlated with the restriction of forest. Over the hundred years for which we have information there does not seem to be any suggestion that the density of bats has decreased in unmodified forest. Food does not seem to be scarce. It has been suggested that increased predation is a major factor in limiting numbers but there is no good evidence supporting this view. Therefore it is suggested that the low numbers are not to be interpreted in terms of changes during the period of current knowledge, but rather as a result of long-standing factors. The possibility that low fertility or high mortality occur should be investigated, and accordingly studies of bat roosts are most desirable.
Skeletal material of bats is occasionally found in caves. This may be used for the identification of the two species. The very short (about 1.3 cm.) broad skull of C. tuberculatus is readily distinguished from the longer (about 2.0 cm.) and narrow skull of Mystacina. Immediate differences are apparent if the dentition is examined, for although C. tuberculatus has four upper incisors and six small lower incisors between the large canine teeth, Mystacina has only two relatively large upper incisors and a single pair of lower incisor teeth closely crowded between the canines. Two premolars and three molars are present in the upper and lower jaws of each bat but in Chalinolobus the first of the upper premolars is minute and easily overlooked.
A difference exists in the number of vertebrae present. Thus, while
Chalinolobus has only eleven thoracic in contrast to the thirteen of Mystacina. The caudal vertebrae of Chalinolobus are greatly elongated, being half the length of the skull, while those of the short-tailed bat are much reduced.
In Mystacina the presence of three phalanges in the third digit and of accessory talons at the base of the claws provide a further distinction between the species.
Mystacina is represented in New Zealand by two distinct forms. One occurs throughout the North Island and is present in at least northern areas of the South Island, but the other is known only from Stewart Island and a few neighbouring islets. Skeletal differences other than those of size are not apparent between these two groups, but in their external appearance they are clearly distinct. In the absence of a full range of specimens the groups are here considered as subspecies.
The northern subspecies is a small delicately proportioned bat characterised by the length of the ears which reach to or beyond the tip of the muzzle, and by the remarkably prominent, though narrow, nostrils. Total length does not exceed three inches and the wing span is up to eleven inches. Gray's plate illustrates an animal which is clearly of this northern subspecies and this can therefore be provisionally recognised as M. t. tuberculata. In contrast the southern subspecies is larger and extremely robust with a total length of three or more inches and a span up to twelve. It has the ears falling short of the muzzle tip, and has the wide nostrils lying relatively close against the muzzle. Provisionally this subspecies may be recognised as M. t. robusta (Fig. 2). The following remarks may be considered to apply generally for any member of the species unless particular reference is made to the subspecies concerned.
Mystacina is a small bat the total length from the snout to the tip of the tail being two and a half to three and a quarter inches. In contrast to Chalinolobus almost the entire length is formed by the body, the tail being barely half an inch in extent. Nostrils and ears are prominent, and the rough, frosted appearance of the fur contrasts well with the sleek fur of the long-tailed bat. With the exception of the bones of the palm and hand, all
Fig. 1: Mystacina tuberculata, dorsal view. Fig. 2: (a) Head of M. t. tuberculata, ventral view; (b) head of M. t. robusta, ventral view. Fig. 3: Chalinolobus tuberculatus, dorsal view. Fig. 4: Head of C. tuberculatus, lateral view. Abbreviations: AB, antebrachial membrane; ATr, antitragus; BL, basal lobe of ear; C, calcar; E. ear; IF, interfemoral membrane; LL, lip lobule; PCL, post calcareal lobe: Ta, tail; Th. thumb; Tr, tragus.
Body colour varies from light grey, through brown to black, with the underside paler than above. The nostrils, ears and limbs are generally black but may be yellowish in grey forms of M. t. tuberculata. The membranes are usually dark brown or black. The hair comprises a close layer of short wavy underhair, with a sprinkling of longer, coarse overhairs or guard hairs. These guard hairs occur more densely in southern animals. All the hairs are tipped with white and unlike those of most other bats they do not show characteristic scale form. Their outlines are smooth and the scales are distinguished only with difficulty. Around the muzzle a number of stiff black hairs radiate in every direction. Short hairs occur on the ears, on the limbs and on the thickened portions of the membranes.
The crown of the head is raised only slightly above the level of the face, and the conical muzzle is long, obliquely truncated and terminated by the nostrils. The jaws are simple and relatively small, and the eyes are almost concealed by large fleshy lids. Extending well beyond the fur of the head are the simple ears, and arising from within each ear a long attenuate projection termed the tragus extends outwards from the side of the face.
Folds of the wing conceal the upper arm from above. The forearm provides a robust support for the membranes. The stout and somewhat hairy thumb carries a strong claw which bears a small subsidiary talon at its base. The long metacarpal bones of the palm radiate from the wrist and with the fingers of the hand support the wing membrane. The second digit comprises a single rudimentary phalangeal bone, the third has three phalangeal bones, and the fourth and fifth each have two. With the wing fully extended the third and longest digit reaches the full span, and the fifth reaches backwards from the wrist to provide the width of the membrane.
The membranes are remarkable for the thick and leathery appearance of those portions adjacent to the body. Strong cutaneous ridges passing from the sides of the body produce this texture. The ridges of the wing membrane pass over the upper surface of the thigh and are continuous with those of the basal portion of the interfemoral membrane. A reduced antebrachial membrane lies in the angle between the upper arm and the forearm and is similarly thickened. Elsewhere the membranes, while thin, are exceptionally tough and smooth contrasting with the delicate membranes seen in C. tuberculatus.
The thigh and lower leg are short and stout, but the foot is extremely large and the loose skin of the sole is deeply wrinkled. Basal talons are present on the claws of the foot as on the thumb. A weak calcar extends from the heel of each foot to support the posterior margin of the interfemoral membrane.
Only a short basal portion of the tail is included within the thickened part of the interfemoral membrane, and distally the tail extends from the membrane as a short projection curving above it. The membrane when
In bats the forelimbs greatly exceed the hind-limbs in size. These latter generally play but little part in movement and are usually short and reduced. Most bats can only crawl or scramble on the ground. These animals usually furl the wing against the body when roosting, or at the most fold it in some simple manner. However, the Molossidae and the New Zealand Mystacinidae differ from other bats in that peculiar folding processes of the wing enable the forelimb to function fully in walking. These bats crawl of run quite actively by using their wrists.
Mystacina is remarkably agile and will run or climb even over smooth surfaces with complete freedom. The large and adhesive soles of the feet, and the basal talons at the base of the claws provide security when climbing. It is, however, the unique folding process of the wings in which the membranous portions are carried beneath the forearm and against the body, and the strange manner in which the interfemoral membrane may be folded beneath the tail, which facilitate the use of the limbs for walking, and make Mystacina the most ‘sure-footed’ of all bats.
When folded, the delicate portions of the wings are concealed beneath the forearm and within small cutaneous pouches at the sides of the body and along the thigh, so that they are protected from injury by the thick leathery portions which alone remain exposed. The folding process commences with the proximal phalanx of the third digit being turned inwards beneath the membrane. This carries with it the proximal phalanx of the fourth digit and the second (terminal) phalanx of the fifth digit. The short first phalanx of this fifth digit remains extended along the line of the metacarpal. The second phalanges of the third and fourth digits, and the distal region of the terminal phalanx of digit five turn backwards and lie close along the side of the body, between the thickened wing membrane and a cutaneous flap extending from the side of the body. This flap continues on to the thigh and conceals the terminal phalanx of the third digit which is directed outwards along this portion of the hind limb.
The interfemoral membrane is rolled forwards so that it lies close against the body at the root of the tail. Only the thickened basal portion remains exposed. With the wing and tail concealed in this manner the limbs are in no way impeded and can be used quite freely for walking.
C. tuberculatus is a small delicately-proportioned animal characterised by the possession of a tail which is nearly as long as the body, and which for almost its entire length is included in a large interfemoral membrane continuous laterally with the membrane of the well-formed wings. When fully extended the wings may span from ten to eleven inches. The length
Body fur varies in colour from black to reddish- or chocolate-brown, with the head and shoulders darkest, often black, and the underside paler. The pubic region may be yellowish brown. Limbs and digits are generally dark above and pale below, and the membranes appear brown or black. Fur is present over most of the head and body, is represented as bristles on much of the muzzle, and is somewhat sparse in the pubic region. It extends only slightly on to those portions of the membranes adjacent to the body and, with this exception, the limbs and membranes may be described as free of fur. The fine hairs measure up to 7 mm. in length, and under magnification show the peculiar scale structure so characteristic of bats. Unlike Mystacina there is no differentiation into overhair and underhair.
The head is short, broad and moderately hairy, with the terminal nostrils represented as low prominences. The jaws are well formed and may be opened to an angle of nearly ninety degrees; they are characterised by the possession of a small fleshy lip-lobule projecting laterally on each side near the angle of the mouth. The minute eye is almost covered by the well-formed fleshy lids. The ears stand slightly higher than the fur of the head, and lie behind the eyes. They have a small backwardly-directed lobe at the base of the inner margin. The ear tip is rounded and the outer margin of the ear is continued along the face, beneath the eye, as an antitragus which terminates just behind the lip lobule. The more pronounced tragus extends from within the ear above the antitragus. It is narrow at its base but widens above and is rounded distally.
The body is compact, tapering somewhat in front of the shoulders but not conspicuously behind. In both species of bat the short pendent penis in the male makes distinction between the sexes readily apparent.
The bones of the forelimb are, with the exception of those of the thumb, very long and slender. The small thumb projects freely from the wrist and carries a long curved claw. Bones of the palm and hand support the delicate wing membrane, but in contrast to Mystacina no bony phalanx is associated with the second metacarpal, and only two are represented in each of the remaining digits.
A well-developed antebrachial membrane extends between the anterior borders of the humerus and forearm. The extensive wing membrane proper extends from the sides of the body and from the full length of the legs except the toes. It is produced laterally to include the full extent of the fingers as shown in the figure.
In Mystacina the leg bones are short and stout, but in Chalinolobus they are long and slender, and the small foot is turned outwards. The calcar extends from the heel as a strong process, and lies along the posterior border of the large interfemoral membrane to provide support for almost half the length of this border. A small rounded post-calcareal lobe occurs near the base of the foot.
Six species of Chalinolobus are currently recognised and these fall neatly into four groups. C. tuberculatus, C. neocaledonicus from New Caledonia, and C. picatus from northern and eastern Australia and New Guinea form a single group readily distinguished from the three remaining species by the absence of fur on the wing membranes. In their colour pattern and in the form of their skulls members of this group are remarkably alike. Some doubt exists as to the validity of their specific standing.
In the remaining species body fur extends on to the underside of the wing membrane to a line passing from the elbow to the knee, and to a lesser extent it is also present on the upper surface. C. gouldi, the largest member of the genus, with head and body two and a half inches and tail two and a quarter inches, is represented in Australia generally, and occurs on Tasmania and Norfolk Island. It is distinguished by the presence at the mouth corner of a vertical skin tag which is an extension of the antitragus. The small C. rogersi is characterised by its hoary grey appearance, and by the absence from the upper tooth row of the minute first premolar found in other members of the genus.
C. morio, which at one time was confused with the New Zealand C. tuberculatus, is certainly more distinct from this animal than is any other member of the genus. It is a small chocolate brown bat occurring in Tasmania and south-eastern Australia, and differs markedly from others of the genus in the absence of the basal ear lobe, in the pointed ear tip and tragus, and in the larger postcalcareal lobe which is supported internally by a minute arm of the calcar.
I would like to express my appreciation to the Directors of the Dominion Museum and the Auckland Institute and Museum who have made study material available. The New Zealand Deer Stalkers' Association has actively co-operated in obtaining many recent records and observations from members throughout New Zealand. The New Zealand Speleological Society has located useful skeletal material and Miss P. Lewis has made available the details of four years’ regular observation. I am indebted to numerous other persons for their assistance in collecting data and to Professor
The gulls and terns are together a well-defined suborder, broadly divisible into the two families Laridae and Sternidae. There are distinctive tropical representatives which are cosmopolitan, and a complex of more differentiated forms in the temperate and sub-polar zones of both hemispheres. Several of the northern forms are transequatorial migrants and occur as non-breeders in the southern hemisphere. None of the New Zealand breeding forms is strongly endemic, although Sterna striata and Sterna albistriata are not known to breed elsewhere.
Because of the distinctive juvenile, subadult, summer adult and winter adult plumages, it is not practicable to present identification data in a single key. The method here followed is to give the salient points of field identification for each phase of each species, and to provide enough diagrammatic figures to emphasise these.
We are concerned with only three species of this family and no stragglers.
2 Wing (upper surface) of adult red-bill gull.
3 Red-Billed gull.
4 Black-Billed gull.
5 Wing (upper surface) of adult black-billed gull
In distinguishing the above two small Gulls, it is roughly correct to say that the young of the Red-billed Gull has a black bill, and the young of the Black-billed Gull has a red bill. There are slight differences in stance and flight that become more apparent after careful field study.
Identification here is more difficult, for not only are there the same age and seasonal plumage phases as found in Gulls, but there is also the vagrant occurrence of northern hemisphere and tropical Terns, mainly during the southern summer.
7 Black-Fronted Tern
8 White-Fronted Tern
9 Caspian Tern
10 White-Winged
11 Black Tern (after Fleming)
Other tropical Terns that have been recorded as stragglers are:
Another related family not dealt with in this review comprise the Skuas (Stercorariidae), comprising two southern forms of the Great Skua and two northern Skuas on migration.
The compound word, mycorrhiza, was coined in 1885 by a German botanist to describe a compound organ which he had found prevalent in forest trees. As the name implies, the organ is a combination of fungus and root and in many plants takes the place of roots. Several types of mycorrhizas exist differing in the morphology of the organ and of the fungus.
Ectotrophic mycorrhizas are obvious as such to the naked eye. Fungal mycelium becomes woven round the root at an early age like a glove round a hand and extension of the root occurs inside the weft of mycelium, or mantle as it is called, which grows to accommodate it. Growth of the root is reduced in length but its branches become more numerous and are stouter than those of uninfected roots (Pl. 2). Part of the additional thickness is due to the fungus mantle and part is due to the greater radial length of the epidermal cells. Thus a non-mycorrhizal root of Nothofagus menziesii has a radius of approximately 160μ while a mycorrhiza on the same species can have a radius of 22μ including a mantle 30μ thick (Pl 1). The hyphae intrude between the epidermal cells and surround each cell with a network usually only one hypha in thickness - this is the Hartig-net, named after its discoverer. Typically the fungus does not penetrate further than the epidermis and only occasionally enters the cells themselves. In some, however, penetration is frequent and these are termed ectendotrophic mycorrhizas.
Ectotrophic mycorrhizas are formed by basidiomycetous fungi, Polypores (e.g. Boletus), Agarics (e.g. Amanita) and puff-balls all being involved. The frequent occurrence of fruiting bodies of these fungi around the base of beeches, oaks, poplars and pines is due to the concentration of the mycelium around the roots of these plants. Not many other plants form ectotrophic mycorrhizas - willows and eucalypts have them occasionally.
Some 90% of the remaining plants from the Thallophyta to the Spermatophyta carry endotrophic mycorrhizas, some with great consistency, others much more casually. Obviously some sort of grouping it required and indeed is easily arrived at.
(a)Orchid mycorrhizas. Although orchids vary from those that grow on soil to those that grow epiphytically on trees, from those with chlorophyll to those lacking chlorophyll at all stages of growth, from those with roots
The fungus which infects orchids is placed in the form genus Rhizoctonia and much has been written on the relationship between the two organisms. In all cases the fungus invades the cortical cells of the organ, all hyphae being within the cells, but is kept in check by some form of defence within the orchid. Thus hyphae may become enclosed in cellulose, fungicide may be excreted by the cells, or cells immediately round the infection may die and thus restrict the spread of the endophyte. Typically the hyphae are digested by the host cells and obviously represent a gain to the host.
The morphology of the fungus is best described by taking a specific example. Earina autumnalis is a native epiphytic orchid, the roots of which are invariably infected by Rhizoctonia (Pl. 1). The fungus enters the velamen and ramifies through it before entering a transfusion cell in the exodermis on its way to the cortex. Once in the cortex the hyphae form coils, or pelotons, within the cell— a characteristic feature of orchid mycorrhizas. As the hyphae age moniliform filaments arise which are typical of the fungus Rhizoctonia (Pl. 1). In many of the cortical cells the hyphae are obviously disintegrating as a result of intra-cellular digestion.
(b)Ericaceous mycorrhizas: Described first in 1885 the mycorrhizas of the Ericaceae and Epacridaceae have never ceased to be a fruitful subject of investigation. Almost without exception the members of these two families possess very fine roots which are converted to mycorrhizas by invasion of the outermost layer of cells by a tangled mass of fine hyphae (Pl. 2). At first the hyphae are too fine for cross walls to be seen, if indeed they do exist at this time, but as the hyphae age they become thicker and septa are then apparent. As is common to all mycorrhizas the hyphae do not penetrate the root apical meristem but infection begins just behind this region. In the older parts hyphae undergo degeneration and the contents are released into the host cells.
The identity of the endophyte remains a subject of continuous controversy and one that is hampered by the extreme difficulty of isolating the fungus, growing it in aseptic culture and back-inoculating the mycelium into sterile seedlings. At the moment an Imperfect genus Phoma, two
Top— Left: Inflated hyphal segments in the cortical cells of Earina autumnalis (X 320). Right: T.S. velamen and outer cortex of Earina autumnalis. Note hyphal disintegration in the cortex (X 100). Centre— Left: T.S. mycorrhiza of Nothofagus menziesii. Right: T.S. non-mycorrhizal root of Nothofagus menziesii (both X 250), (m, mantle; ep, epidermis; c, cortex; en, endodermis). Bottom— Left: Arbuscule in cortex of Tmesipteris tannensis (X 230). Right: Intercalary vesicle in root of Clematis indivisa (X 280).
Pythium and Mortierella, and a sterile septate form genus have all been proposed as endophytes.
(c)Vesicular-arbuscular mycorrhizas. In a survey of the roots of plants growing in New Zealand it has been concluded that about 90% carry endotrophic mycorrhizas of this general type. Some have all their roots always infected, e.g. Griselinia (Pl 2), others have a sparser rather less constant infection, e.g. Coprosma, while still others are only occasionally infected and then very sparsely. Fungal infections of this general type have also been described in Ginkgo, ferns (mycorrhizomes), Psilotum and Tmesipteris, Lycopodium prothalli (mycothalli) and liverworts.
Hyphae of the fungal component of these mycorrhizas ramify through the cortex but as in all mycorrhizas they do not enter the stele. Within the cells they may form a coil or they may run straight through, but characteristically they anastomose to form a closed network. The characteristic structures of the fungus are the vesicles and arbuscules. Vesicles are spherical but may become irregularly shaped due to confinement in the relatively small space of a cell. They usually develop terminally (Pl. 2) on the hyphae, but in some cases a swelling occurs along a hyphae (e.g. Clematis, Pl. 1). They are not cut off by a septum. The contents of the vesicle become rounded off into spore-like bodies (Pl 2) which, however, soon disappear along with the wall. Occasionally when a hypha enters a cell it forms a profusely branched tree-like organ, an arbuscule, the small ultimate branches of which disintegrate, followed by disintegration of the walls of the whole structure (Pl. 1). At this stage the hyphal protoplasm is set free in the cell but it soon disappears and the cell protoplasm remains unaffected by the whole process.
The endophyte in these mycorrhizas has been placed in the Phycomycete genus Rhizophagus.
Mycorrhizas and root hairs are mutually exclusive. Thus in ectotrophic mycorrhizas there are no root hairs and they are also absent from heavily infected endotrophic mycorrhizas such as Pernettya (Ericaceous) and Griselinia (Rhizophagus). In the more lightly infected roots they may be
Top— Griselinia littoralis seedlings grown in an infertile soil. Mycorrhizal seedlings on left (3), non-mycorrhizal seedlings on right (6). Centre— Left: Pinus radiata seedlings grown in an infertile soil. Left, non-mycorrhizal; right, mycorrhizal. (X 1/6.) Right: T.S. root of Griselinia littoralis showing zone of Rhizophagus infection (X 45). Bottom— Left: Vesicle in root of Podocarpus hallii (X 1,000). Centre: Typical mycorrhiza of Nothofagus menziesii (X 3). Right: T.S. mycorrhiza of Pernettya macrostigma showing hyphae confined to outer layer of root (X 490).
The literature in this field is an object lesson in the danger of making generalisations. There are many mycorrhizas, all fundamentally the same admittedly, but differing in important physiological respects and even on the same plants differing according to the environment it happens to be growing in. It is small wonder then that every possible explanation of the function of mycorrhizas has been offered and that many of these are almost diametrically opposed. We will try to see some order in this chaos.
The physiology of mycorrhizas can be described by answering three questions:
It has been found for ectotrophic mycorrhizas (which have been studied widely in this respect) that the density of infection bears an inverse relationship to the fertility of the medium in which the plant is growing. In the few endotrophic mycorrhizal plants which have been investigated in this regard the same thing holds. At one time this was regarded as sufficient reason for the formation of mycorrhizas, i.e. that mycorrhizas were most abundant where they did most good. But a more rational explanation was wanted. It had been noticed that ectotrophic mycorrhizal infection was reduced when plants were grown in shade. That this was an effect due to the reduced carbohydrate status of the roots was substantiated by ring-barking plants growing in good light, thereby cutting off the supply of carbohydrates from leaf to root and demonstrating that infection was again decreased. The effects of shading on infection could be somewhat counteracted by supplying sugar to the plant or by lowering its supply of nitrogen. The hypothesis was put forward that mycorrhizas are formed if the host roots contain a surplus of soluble carbohydrates. It was further assumed that a deficiency of nitrogen and/or phosphorus in the host plant would retard the formation of amino acids and proteins from carbohydrates and these latter would thus accumulate and stimulate mycorrhizal formation. Manurial experiments have shown quite conclusively that a shortage of either nitrogen or phosphorus enhances mycorrhiza formation whether the mycorrhiza is ectotrophic or endotrophic. This theory, which we owe to a Swedish worker, Bjorkman, in one stroke provides an explanation for the known frequency of occurrence of mycorrhizas and explains what the fungus gains from the association. Somewhat substantiating this theory is the fact that mycorrhizal Basidiomycetes characteristically cannot break down higher carbohydrates such as cellulose and therefore depend on a supply of simple carbohydrates.
At this point I should make it clear that the foregoing does not apply to orchid mycorrhizas. There the boot is precisely on the other foot. It was shown that seeds of all orchids, with but two or three exceptions, would not germinate in the absence of a mycorrhizal fungus. Seeds of orchids are extremely small— up to 3,000,000 being produced in one capsule— and they therefore contain little food reserves. It was further shown that the vast majority of orchid seeds could be made to germinate in the absence of the fungus if soluble sugars were supplied in its place. It is known that Rhizoctonia unlike some other mycorrhizal fungi can excrete cellulytic enzymes and the conclusion seems justified that the fungus supplies soluble carbohydrates to the host in this particular case. It is tempting to ascribe a similar function to the endophyte of the colourless gametophytes of Lycopods, Psilotum and Tmesipteris; indeed it is difficult to perceive what other means these may have of obtaining carbohydrates. In a few orchids seed germination depends upon the provision of accessory substances as well as carbohydrates.
To the question— what does the fungus gain from the association— we have supplied one, if not the only answer. Literature on this point is sparse but again most of the work in the field has been done with ectotrophic mycorrhizas. Obviously until we know the growth requirements of endotrophic mycorrhizal fungi, and this has as a prerequisite the growing of the fungus in pure culture, we are only guessing. This is not the case with ectotrophic mycorrhizal fungi. Many such fungi are heterotrophic for specific vitamins, especially thiamine, and in addition there are growth stimulating compounds obtained from forest litter and forest tree roots which have, however, not yet been identified.
We are probably justified therefore in picturing mycorrhizal fungi as obtaining simple carbohydrates and some accessory compounds from the roots that they infect.
The case for heterotrophic orchids has already been answered, but what about the remainder? There can be little doubt that under specific conditions mycorrhizas mean the difference between certain death of the plant and normal healthy vigour (Pl 2). These conditions are those of nutrient starvation. In forest soils and in dense turfs, where root competition is fierce, in very infertile soils and in root-bound condition in a pot, mycorrhizas will show their greatest effect. In this respect the availability of phosphorus appears to be all important with nitrogen suspected of being fairly important but the other essential elements of doubtful significance.
Pines, with their relatively high growth rate, are good experimental plants and most of the work concerned with mineral nutrient uptake by mycorrhizas has been done with these plants. Thus many experiments have compared by chemical analysis the mineral content of mycorrhizal and non-mycorrhizal plants after a period of growth in infertile soils. These
Although some of the theories of the mechanism of enhanced nutrient uptake due to mycorrhizas are not specifically concerned with phosphorus uptake they must be capable of explaining the outstanding effect of mycorrhizas on absorption of this element.
Early in mycorrhizal literature it was proposed that the effect of mycorrhizas was due to their greater absorption area as compared with non-mycorrhizal roots. It was pointed out earlier that mycorrhizas were of greater diameter and were more branched than non-mycorrhizal roots so that per unit length mycorrhizas would present a much larger surface to the soil than non-mycorrhizal roots. But it was also pointed out that mycorrhizas do not extend as much as non-mycorrhizal roots and it has been calculated that this at least compensates for the increase in other dimensions.
The theory that mycorrhizal plants have a greater transpiration rate than non-mycorrhizal plants has never been popular and lacks confirmatory evidence.
More recently it has been proposed that mycorrhizas excrete more H + ions than non-mycorrhizal roots due to the known greater metabolic rate of the former. It is argued that these ions will release greater quantities of bases from base exchange material in soils and thus increase the uptake of the bases. Similarly it has been shown that bacteria and fungi excrete organic acids into the substrate and these acids act as chelating (solubilising) agents for insoluble phosphorus.
It is claimed that this is the means of increased phosphorus uptake by mycorrhizas over that of non-mycorrhizal roots.
In the last few years radio-active phosphorus has become a major tool in solving this problem and advances have certainly been made with it. Thus we now know that the effect of temperature, metabolic poisons, and the course of phosphorus uptake by the host plant over short periods of time all demonstrate that phosphorus is actively (metabolically) absorbed by the hyphae in mycorrhizas before being passed on to the host.
In addition the fungus acts as a reservoir of stored phosphorus for the host since removal of mycorrhizal plants to a medium entirely lacking in phosphorus does not substantially alter the rate of phosphorus absorption by the host from the fungal hyphae. Non-mycorrhizal plants lack this
The growth of some ectotrophic mycorrhizal fungi in pure culture is stimulated by the addition of amino acids which they are able to utilise better than inorganic nitrogen. It has also been shown that hyphae will transfer organic nitrogen compounds from an isolated source to pine seedlings. This has been interpreted as showing that mycorrhizal fungi in forest soils are able to absorb and break down organic nitrogen compounds and provide the host with otherwise unavailable nitrogen since in such soils there is intense competition for the small amount of inorganic nitrogen available there. But the evidence is less strong than that showing enhanced uptake of phosphorus by mycorrhizas.
In orchids we believe that fungal infection is necessary for seed germination by virtue of the carbohydrates supplied. In heterotrophic orchids this relationship probably exists during the whole life of the plant but we do not know what part the fungus plays in the nutrition of adult autotrophic orchids.
In ectotrophic, and in those intensely infected endotrophic mycorrhizas which have been experimentally studied, conditions combining maximum photosynthesis with a mild deficiency in some mineral nutrients induce the greatest infection. In these same plants, the presence of mycorrhizas can overcome a deficiency in phosphorus which would mean death to plants lacking mycorrhizas. Mycorrhizal fungi are also suspected of supplying the host with nitrogen derived from the soil's reservoir of organic nitrogen.
The conditions producing maximum infection or the degree of essentiality of mycorrhizas have not been assessed for plants in which mycorrhizal infection is not intense or constant.
I wish to thank Professor G. T. S. Baylis and Mr. R. F. R. McNabb for permission to use some of their research material and diagrams in this review.
The scientific name of this insect is Bolitophila luminosa. Some years ago the name was changed. I think on unsatisfactory grounds, to Arachnocampa luminosa— so let us call it B. luminosa. This insect belongs to the group of fungus flies, Mycetophilidae, sometimes called shade-flies because they like damp shaded situations. Most of the larvae of these fungus flies live on damp rotten vegetation, or they bore in fungi such as mushrooms. In the British Isles it is difficult to find an old mushroom which is not being tunnelled by small white mycetophilid worms. From such lowly ancestors our glow-worm is descended. The first European scientist who noticed the glow-worm was Meyrick, about 1880, who saw it on the banks of a stream at Auckland. Meyrick thought the light came from the head end, whereas we know it comes from the tail end. Meyrick had noted the peculiar snare that this insect makes, and he rightly thought that the glow-worm might catch insects and eat them, as do spiders. Most other well-known fire-flies, or luminescent insects, are beetles, belonging to the family of which the click beetle is a member.
The distinguished New Zealand entomologist B. luminosa produced the light, but in 1915 two Americans, Wheeler and Williams, had, after a visit to this country, taken some glow-worms home in a bottle of methylated spirit, and they correctly stated that the light organs were the swollen ends of the malpighian tubules (Fig. 1, L). Malpighi was a famous Italian anatomist of the Middle Ages, and his name is also linked with a part of the vertebrate kidney. In almost all insects waste matter is stored up in from four to eighty or a hundred malpighian tubules which connect to the insect gut where the mesenteron (stomach) and intestine join. Before an insect like a butterfly pupates, these stored-up waste urates are cleared out via the intestine.
The discovery of Wheeler and Williams was all the more remarkable as there seems to be no reason why part of the malpighian tubules should become so modified as to be able to produce light. In the beetle fire-flies,
B. luminosa
About 1892, Albert Norris showed that the glow-worm was predaceous and carnivorous, and the snare was used to capture insects which had been attracted by the light. That this is true was finally proven by Wheeler and Williams in 1915, when they found pieces of chopped-up insects in the mesenteron of the glow-worms (Fig. 1, M).
Those who examine the snares of glow-worms living outside on river and creek banks, will notice that there is a curtain of hanging or vertical silken lines which are fastened beside a more or less horizontal silken runway on which the worm lies (Fig. 3). If you touch the snare the worm rushes immediately into a tunnel or crack (HP) into which the runway is continued. If you now carefully cut away the side of the tunnel you will find the worm still glowing, but it soon douses its light. Thus it can retreat into its hiding place in about three seconds, and this covers its light. People have thought that the worm can douse its light in a matter of seconds, but this apparent almost instantaneous dousing is due to its retreat into a crack or tunnel. We will return to this matter later.
The vertical hanging snare lines (Fig. 3, SL) are usually about an inch long; but in miners’ abandoned shafts, and in caves, these lines may be twenty-four inches long. On banks, the worms usually live in sheltered places, and they hang lines longer than an inch, if they have found that wind does not tangle up their net. The vertical lines have regularly placed droplets of mucus on them, so as to give the appearance of a string of beads. This mucus helps to entangle insects which fly against the curtain. One snare photographed years ago by Dr. Salmon had more than forty vertical lines. The larger the snare, the better the chance that it will catch food. Albert Norris said that the horizontal line in which the worm reposed was really a tube. It is true that the worm in this position is itself covered with mucus and silk, which resembles a tube. In the case of the wheel-like web of the spider Epeira. the spokes of tension lines are of plain silk, but the spiral lines of this snare have little sticky droplets. In this case the spider spins a silk line, and as it hardens, a gland covers the silk with a thin sticky substance which by surface tension becomes resolved into a single chain of droplets. It was thought that the droplets of the snare of B. luminosa might be so produced, but recent observations seemed to have shown that the worm emits a single thread, waits, and then spews out of its mouth a droplet of mucus the correct size. Then the silk line is continued, then another mucus droplet is put in place, and so on. When a chain of the right length is produced, it is held by the larva, and then stuck in the right place, at the right distance from other already spun vertical lines. Thus this insect is able to judge distance. If you sweep away the vertical curtain with a stick, the worm will that evening begin to make new lines, and will finish the job in a night or so. The very long lines seen in curves each probably represent the capacity at one time for secretion of the
Epeira can make a whole new web in about twelve hours, and the glands of B. luminosa are comparatively very large.
Now as regards the anatomy of the larva, Gouri Ganguly, an Indian woman zoologist who studied these larvae at Dublin, found that the two tiny thumb-like papillae at the end of its body contained chordotonal organs. These are peculiar sense organs found in various parts of the anatomy (usually on the legs) of insects. They are sense organs designed to register vibrations, and they consist of an arrangement like an elastic thread on which are wrapped sense cells (Fig. 2, SC). The struggles of insects which have been caught by the vertical fishing lines are thus noted by the glow-worm, which at once climbs down these lines and kills the insect with its powerful jaws. The struggles of the captured insect, and the descent of the glow-worm, make a muddle of the snare, but this is later straightened out by the larva. The latter just sucks out the blood of its prey, and if food has been scarce, as it must be in caves, the larva with its mouth-parts carefully saws the body and legs of the prey into the right size for swallowing whole. If there has been a good supply of food, the larva chops up only the juicy parts, and discards the harder regions of the prey.
When the larva is about a little more than an inch in length, it is full grown, and it now makes preparations for pupation. These have rarely been seen, and never properly described. We believe that the larva clears away all its vertical sticky lines and releases one end of its horizontal runway, so that it hangs in a bare space under a bank, or from the roof of a cave. It now sloughs off its larval skin, and becomes a hanging pupa.
Figures
Figs. 1-4. All figures semi-diagrammatic.
Fig. 1: Larva showing main organs. Fig. 2: Chordotonal sense organs in anal palp (P), in Fig. 1. Fig. 3: Plan of typical snare. The luminescent organ is on the left, head on right. The runway (RN) leads into the hiding place (HP) on the left. Fig. 4: Plan of recommended arrangement for keeping larvae for observation. Rotten branches are braced together, bark left on, or holes made for hiding places. Glass cover is essential. Rotten branches can be kept damp more easily than new ones, or than stones. Old cement slabs are also good.
Lettering
B, brain; D, culture of fruit flies (Drosophila) in banana; H, head; HO, curved sensillary seta; HP, hiding place; J, jaws; M, mesenteron or stomach; MG, mucus gland; MP, 1, 2, 3, 4 parts of the malpighian tubes, No. 4 (L) being the light organ; N. nerve from chordotonal sense organs; O, oesophagus: OV, oesophageal valve; P, anal papilla; R, rectum; RN, horizontal runway; S, silk gland; SC, cells of chordotonal sense organ; SL, vertical fishing lines with mucus droplets; X, position of nerve ganglion enervating the segment with the light organ.
It is known that this pupa is occasionally luminescent. After a time, said to be three weeks, the adult insect emerges. The imago is something like a dark mosquito, but is much bigger. If you find a midge-like insect, body 17 mm. long, wing span 20 mm., antenna 4 mm., inside a cave, mining shaft, or under a wet bank where glow-worms live, it is likely to be the adult B. luminosa. Likewise if you find a hanging pupa 7-10 mm. in length in the same places, it is a glow-worm pupa. The Tanypus or chironomid midge which is often found in such localities is only 8 mm. body length, and is brownish. The glow-worm adult's abdomen has dark and light intersegmental parts and is unmistakable. Its wings are sooty at their outer ends.
It was stated by
The larva or glow-worm has a large nervous system consisting of a brain, a ventral nerve chain, and nerve ganglia in each segment except the last. We know that the chordotonal organs and muscles of the last segment have nerves going to and coming from the last abdominal ganglion in the seventh segment, but we are not yet certain about the innervation of the light organ. Recently some experiments have been made on the control of light by the glow-worm. If the head of a luminescent worm is cut off, the light goes off. The same takes place if the body is cut away above the ganglion in the seventh segment. If, however, the light organ is isolated from the seventh ganglion by a cut, the light comes on.
So far as we know, what actually happens during the life of the glowworm is this. When night falls this is noted by the larva's eyes; the latter are small, but capable of registering light waves. A stimulus from the brain is sent down via the central nerve cord to the ganglion in the seventh segment, and some sort of reaction here raises the block which has prevented the light from turning on. It is generally believed that the deprivation of O2 keeps the light organs from functioning, but how this is brought about in B. luminosa is not under stood. Further careful anatomical examination, which is being undertaken, may help to explain this.
There are many readers of this article who can help in solving some of our problems about the New Zealand glow-worm. If you live near glowworm caves, shafts, or banks, here is what you should try to do. Get some waterproof tags such as gardeners use, go out at night with a flash lamp, and put a tag and date near the biggest glow-worms you can find. Visit these places at least once a week to find the pupae when the worms pupate. These can be brought home and kept hanging in a damp, wide-mouthed,
Finally there is the question which everyone is bound to ask— how did it come about that the descendant of humble fungus larvae changed from a fungivorous life to a predaceous one? How did the physiological changes in the ends of the malpighian tubes arise, and finally, how did the larva learn to make a clever snare?
But these questions are similar to many which can be asked of other animals and plants. How, for example, did various molluses depart from their sedentary life and swim with the best of them in the ocean? It is true that other fungus flies have developed in a smaller way the peculiarities of B. luminosa. When I was a student we were taught to believe the Darwinian Theory of Natural Selection. Nowadays there are many biologists who find this theory unsatisfactory, but truth to tell the other theories seem equally difficult to believe. Another fungus fly (Ceroplatus) has the power to produce light, but not from its malpighian tubes; the light in this case comes from the fat body. This denotes a major physiological change in the metabolism of the fat cells; but how did these insects Ceroplatus and Bolitophila find that this capacity to produce light could be used to attract food, and how did this apparently chance physiological change come to be transmitted to, and used by its descendants? The Mutation Theory postulates that these major changes took place by comprehensive steps suddenly, which is not easy to believe. These major changes in Bolitophila are so many that it is not possible to believe that they all came at the right degree of development, and at the right time to produce the glow-worm as we know it to be today.
The Lamarckian Theory still has its adherents. It seems possible that, the behaviour and bodily changes of the animal during its life could be impressed on its germ cells and so transmitted to its descendants.
Here are some other problems which need solution:
For fixing pupae for anatomical examination, Carnoy's fluid is suitable. It is equal parts of chloroform, glacial acetic acid and ethyl alcohol. Leave pupae in this for two hours, then store in 90% alcohol. To send adult insects, put a little cotton wool in the bottom of a tube, then put in the insect, then a wad of cotton wool so as to leave the insect in a good space, then cork.
It is unfortunate that many classical aspects of Zoology are rarely studied from the living animal. Text-books with their intimate descriptions have isolated students from actual contact with the processes which the texts describe. Reference to the text seems so much easier than the study of the animal itself, but too frequently the study only of the text leaves the student with a confused understanding and no real appreciation of the subject matter.
Aristotle obviously studied the development of the chick from incubated eggs. Two thousand or so years ago, Aristotle had a more vivid picture of the embryology of the chick than does the average student of this day who knows the subject only as words and pictures in a book. Aristotle must have borrowed the eggs from an incubating hen. He lived probably closer to nature than many of us are living in this day.
Nevertheless it is now a simple matter to obtain fertile eggs from a poultry man. We can place these eggs in a shoe box with straw, warm them gently with a 15-watt electric bulb so that they are kept at a temperature of about 38°C. and then the eggs will develop. If we obtain a dozen fertile eggs, four can be placed in the box one day; four on the next; and four on the third day. The eggs should be marked so that each can be recognised as to the length of its incubation.
On the fourth day, remove the eggs which have been incubated for twenty-four hours. Make a solution of one teaspoon of common salt in one quart of water. Warm this to 38°C. Tap and break the upper surface of the egg to make a hole about one inch in diameter. Tease away the fragments of the shell. With scissors cut away the membrane and gently lower the egg into the warm salt solution so that the egg is covered.
New use a lens. You will see the developing disc of the embryo with a streak on the surface which will become much of the nervous system.
Do this with an egg which has been incubating for forty-eight hours. This will show the forming vesicles of the brain, the spinal cord with muscle buds obvious on either side all prominent on the disc. It may show the rudiment of the eyes, the head beginning to lift from the surface, blood islands and many other details in a reality never to be known only from the text.
The egg which has been incubating for seventy-two hours will show a large head with prominent brain vesicles, many muscle buds, the early forms of the embryonic membranes, a beating heart and flowing blood.
If you would proceed further then cover the egg with the salt solution, gently cut around the edge of the disc to float the disc free from the yolk and float it carefully on to a submerged slide. Raise the slide from the solution. Flood the disc with salt solution. Dry the lower surface and put on a cover slip.
This preparation can be studied with the lens or microscope, drawn in all its detail, and the development of the chick becomes a study of life and no longer a matter of simple memory. This is the time when reference to a text has real value.
There is only one caution to keep in mind. See that the lamp for incubating the eggs is secured so that it cannot overheat and kill the eggs nor be a cause of fire. This is a hazard which was no worry to Aristotle.