By G. M. Thomsom
Read before the Otago Institute, 11th June, 1878

The following notes drawn up from jottings made during the past spring and summer, are by no means exhaustive, but may rather be looked upon as a small contribution to our already existing information on this interesting subject.

Of the eleven genera which are represented in this part of the island, I have made more or less lengthened observations on ten, viz.: Earina, Dendrobium, Corysanthes, Microtis, Caladenia, Pterostylis, Chiloglottis, Lyperanthus, Thelymitra and Prasophyllum. I was not fortunate enough to obtain specimens of Gastrodia, which is a very readily overlooked plant.

Some of my specimens were cultivated, and thus yielded more certain information than those which were examined in the wild state.

One fact which has struck me during these investigations is, that I have hardly ever been able to capture insects carrying pollen on any part of their body. Only when examining beds of Corysanthes have I found insects with pollinia. It is possible that the general coldness of the past season, and the remarkable scarcity of all kinds of insects, have had a good deal to do with this. If this is the case, of course a disturbing element has been introduced to some extent into my observations.

Both this species and C. rivularis were examined by me, but the flowers are almost identical in structure, the difference not affecting the relations of the parts. They are very striking in appearance, owing to their lurid purple colour, and the long twisted sepals and petals, which give them an extraordinary resemblance to a large spider sitting on a leaf. The upper sepal is large, prominent, and helmet-shaped, and projects forward over the flower. The labellum is large and involute, almost semi-cylindrical, with its external margin fimbriated and expanded downwards into a longish tip. It is not attached continuously at its base. On each side of the flower, when in bud, a small slit is seen, which widens by an expansion of the margin (which is thus caused to arch slightly outwards) into a small circular aperture. By the contact of the in-turned edges of the labellum, and the overlapping of the upper sepal, a horizontal aperture is left in the mouth of the flower, which bends at right-angles a little way in, and opens into a tolerably large cavity. Placed quite at the bottom of this is the short, thick column, lying almost horizontally in C. rivularis, and somewhat more erect in C. macrantha. The stigmatic cavity is deep, and on its posterior margin is the rostellum. This is formed of large cells, covered with a very delicate membrane. If this be touched with a bristle, it is almost instantly ruptured, and a small, very viscid drop of matter exudes. In withdrawing the bristle the pollinia are brought away with it. The anther is terminal (posterior), and has broad lateral projections. The pollinia are four in number, in two pairs, and in the form of plates. The flowers do not appear to secrete any nectar, but when the surface of the labellum is slightly punctured, a considerable amount of sweetish purple juice exudes, which is probably grateful to insects. From the shape of the flowers, it is necessary to cut them longitudinally to see the parts. Looking at the position of the anther and stigma, it appears to me almost impossible that self-fertilization can take place; at the same time it is somewhat difficult to suggest any satisfactory way in which an insect could accomplish either this or cross-fertilization. I presume that any insect entering the flower would have to back out again by the same way as it entered, and in doing so it would come in contact with the rostellum, and would remove the pollinia on its head. It is also probable that, in endeavouring to obtain from a second flower any of the sweet juices from the tissue at the base of the labellum, it would slightly advance its head, so as to bring the pollinia attached to it on to the stigma. Again, it is possible that self-fertilization might be secured by an insect thus getting the pollinia on its head, and then endeavouring to push its way down through the small lateral apertures. In doing so, it would almost certainly smear the stigma with pollen from the same flower, and I have sometimes been inclined to think that such did take place. At the same time, this would seem like putting an unnecessary difficulty in the way of what is usually a very simple process, and therefore no great value is to be attached to this idea.

For a time I could not understand why spiders frequented these flowers so much, but I soon found a sufficient cause. The only insects capable of removing pollen which were found about the flowers were small Diptera—probably a species of Culex. In several cases these small flies had penetrated into the tube of the flower, and, in their eagerness after the sweet juices found there, brought their heads in contact with both rostellum and stigma, and partly owing to the viscidity of these parts, and partly to the narrowness and bending of the tube, were unable to withdraw backwards. In some flowers insects were thus found still alive, in others they were dead, while in many others only portions of them, such as legs, wings, etc., were left, the spiders having devoured the rest. In every case in which a captured insect was withdrawn from its trap, the pollinia were removed also, securely attached to the front of the head.

I closely examined 143 flowers, and found that in 47 the pollinia were still in the anther cells; from 90 they had been removed, while in 6, dead or living insects were found glued to the stigma. Of the whole number examined, only a small proportion ultimately produced capsules.

The flowers of this genus will well repay examination.

In the flowers of this species the column is protected by a broad, flat hood, formed by the posterior sepal and the two lateral petals. The lateral sepals are completely reflexed, and lie back against the ovary. The labellum is large and pendulous, hanging out from the front of the flower like a tongue. It is rectangular in shape, rather longer than broad, with the margin crimped and curled, and bearing three glandular projections on its surface. Two of these are situated together near the base, and enclose a small depression or pit. This, from its position and appearance, I take to be a nectary, but I was unable to detect any liquid in it. The third gland is formed by an irregular wart-like mass of cells, and is situated near the apex of the labellum. I have not investigated its functions, nor do I know how its presence can be accounted for. The column is very short, and stands almost square, this appearance being caused by the wings or auricles which stand up on each side. Beneath these is the hooded anther, enclosing four pollinia, which lie very loosely in their cells. They present the appearance of two masses, but each is composed of a large outer and a smaller inner sheet, of a reniform shape, united by their threads to a short caudicle. In front of and somewhat below them is the viscid rostellum, towards the apex of which a minute white point is visible, which marks their point of attachment. The rostellum projects considerably outwards, so that the stigmatic surface is placed in a recess. The slightest touch on the viscid disc suffices to bring away one or both pollinia, the matter being excessively viscid. An insect alighting on the rostellum, and advancing its head to examine the glands at its base, would be certain to touch the rostellum and bring away the pollinia. These fall slightly by their own weight, so that on entering a second flower, they would be in such a position on the front of the insect's head as to touch the stigma immediately under the rostellum. In the first spike examined by me, 83 flowers were fully opened, and all but the top one had their pollinia removed.

Even when not fertilized by insects however, these flowers are readily self-fertilized, and during the past season this appears to have been the case with the great majority. After a time, the pollinia appear withered and brown, and somewhat dragged forward from their anther cells, while the ovary begins to enlarge, showing that pollination has taken place. If such flowers are examined carefully, it will be found that the pollen grains have emitted a great mass of tubes, which penetrate the upper margin of the stigma, thus ensuring fertilization. I found this to be the case in several hundred flowers which I examined. The position of the labellum on the underside of this flower is caused by the usual twisting of the pedicel or ovary, which is so common in many orchids. But in young buds the posterior sepal is lowest and placed on the side farthest from the axis of the spike; and it is during the gradual maturing of the flower that the twisting takes place, so that, by the time it opens, the labellum and posterior sepal have changed places.

This species, as might be expected from its facilities for reproduction, is one of the commonest plants of the class.

Chiloglottis traversii, Müeller.

This is a most abundant orchid in upland districts as an elevation of 1500 to 3000 feet. The flower is solitary on an erect scape, three to four inches in height. The upper sepal is obtuse, somewhat arched forward, and slightly keeled. The lateral sepals are placed under the labellum, and extend forward almost horizontally. The labellum is broad; on each side of the expanded portion is a yellow-coloured patch bearing two or three brownish spots, while extending from the middle to the base are two rows of yellow glands. The column is long and erect, slightly winged above, and bearing a terminal anther which encloses four pollinia. The stigma is rounded and slightly hollowed out, and is placed in close contiguity to the anther. The arrangement of the parts is so simple that an insect alighting on the labellum and advancing its head into the base of the flower could hardly fail to remove the pollinia; nor could one entering with pollen on its head fail to leave these on the stigma, for in withdrawing pollinia from a flower they are always slightly depressed by the cap of the anther. The pollen of this plant is very incoherent, and the lower surface of the stigma projects a little, so that I am inclined to think self-fertilization takes place in flowers which have not been visited by insects. The majority of the flowers appear to set good capsules, and flowers which I fertilized artificially, produced good full seed-vessels. I examined one sunny day twenty-two flowers growing in the open; of these only three had both pollinia removed; in one the pollinia were removed from one anther lobe; in five others the pollen masses appeared more or less disturbed, while in the remaining thirteen the anthers were untouched.

The fertilization of the flowers of this genus has been so well described by Mr. Cheeseman, in the Trans. N.Z. Inst., Vol. V., p.352, that I cannot well add to it, but my observations on them more than over induce me to cousider that thero has been an unusual scarcity of insect life during the past season. Out of all the flowers of the above species, and of P. graminea, examined, not one had the pollinia removed. The flowers are incapable of self-fertilization. Certain experiments made by me to test whether they were fertile with their own pollen were rendered useless by being conducted in the open, where the flowers were liable to be destroyed.

The rostellum of this orchid, when examined in bud, lies in front of and between the bases of the pollinia, but quite separate from them. At this early stage it consists of an oblong, pearly-white body, composed of large rounded cells, filled with granular fluid. The pollinia stand in a small hollow on the top of the column, and at this stage are attached only by a small posterior ligament at their base.

In this species the flower is solitary, on a short scape, which lengthens after flowering, and is partly covered by an acute, sheathing bract. When fully developed, all the parts stand nearly erect, and thus leave no landing place for insects. The labellum is acutely trowel-shaped, with one broad central, and several narrow, lateral, longitudinal, purple glands. The column is curved back at the base, and then ascends in front of the upper sepal. The stigmatic surface is large, almost circular, quite flat and excessively viscid, there being no distinct rostellum. The anther is terminal, and encloses four plate-like pollinia, which are coherent, and are attached by their bases to the upper margin of the stigma (rostellum). Before the flower is open, and while yet almost sessile, and sheathed by the bract, the stigmatic surface becomes excessively viscid, and smears all the portion of the labellum immediately opposite to it. I could not ascertain how the pollen got on to the stigma, but in the few flowers I was enabled to examinc, all four pollinia were on the stigma, and the anther cells were empty.

From the position of the flower when the parts are ripe for pollination, viz., low down between the two leaves, from its inconspicuous greenish colour, and the fact that viscidity is strongest in the unopened flowers, I am of opinion that this species is exclusively adapted for self-fertilization. The subsequent lengthening of the scape is probably only to aid in the dispersion of the seed.

In this orchid the flowers are solitary, or two on a scape, partially covered by a relatively large concave bract, and of a green colour through-out. The posterior sepal is large and broad, arched forward, and covering the column like a hood. The labellum is flat, broadly ovate and acute, quite glabrous, with two lateral and four median ridges. The column is broad, somewhat arched forward, and terminated by the acute anther. The rostellum placed directly above the stigmatic chamber, impinges on the base of the anther, and is slightly viscid. The pollen-masses, four in number, are very incoherent. From their inconspicuous colour, the fact of their being very frequently closed, and the extreme incoherence of their pollen, I am inclined to think that the flowers of this plant are always self-fertilized. I examined 39 flowers, and found that the pollinia were present in all of them, but in the more advanced some of the pollen was scattered over the stigmas, and the ovaries appeared well-developed.

The fertilization of this orchid is treated of in Fitzgerald's “Australian Orchids,” and quoted by Darwin. All the parts of the perianth, including the labellum, are similar in colour and shape. The column is nearly erect, and slightly hooded at the apex. On its front margin, and a little below the apex, a projection occurs on each side, bearing a tuft of exquisitely beautiful feathery hairs. These are the auricles or staminodia which represent two out of the three stamens of the inner whorl, the third being the only stamen fully developed. In this flower they form a very conspicuous feature, but I do not know their function, if any. Placed quite in at the back and near the base of the column, are the two persistent anther lobes. In very young buds these contain the pollinia, but as they approach maturity they become attached to the back of the stigma, which stands forward a slight distance from the column. The pollinia are composed of four sheets or plates of white, powdery, very incoherent pollen. The rostellum is hardly viscid at all, nor would this be of any use to the plant, as it is seldom, if ever, visited by insects. The flowers are seldom found open, and as a rule are probably self-fertilized. I presume that the pollen grains emit their tubes to the upper surface of the stigma, but I never succeeded in detecting this.

The flowers are small and greenish-brown in colour. The base of the ovary is sheathed by a short truncate bract; the very short pedicel is not twisted, so that, as in Thelymitra, the labellum appears in its normal position above the flower. All the parts of the perianth are similar in form and colour. The column is very short and erect, with the anther placed at the back. At each side rises a small two-lobed appendage, representing a staminodium or imperfect stamen about half the height of the column. The stigmatic surface is broadly triangular, and is protected in front by the labellum, and latterly by the staminodia. The pollen grains are usually found adhering to the back of the stigma, some on its upper edge. When examined under the microscope, some of these were found to have emitted a mass of short tubes. The pollinia are two in number, and the pollen grains forming them are bound together into small wedge-shaped masses. The flowers are somewhat sweet-scented, and though dull-coloured are tolerably conspicuous, but there appears to be no trace of a nectary. Nor from the position of the parts is it very probable that an insect could remove the pollinia, so as to place the loose, incoherent grains on the stigma of another flower. The species is evidently well fitted for self-fertilization. In nine spikes examined by me, containing altogether 75 open flowers, only four appeared to have the pollinia partially removed, and, even in these, pollen grains were adhering to the stigma and anthers.

Imperfect as the foregoing notes are, they still point to the correctness of the general principle that where it is advantageous to a plant to have its flowers cross-fertilized by pollen from another plant, there we find agencies for attracting suitable insects. Thus Earina has conspicuous flowers, sweet scent, and succulent tissue at the base of the flower; Dendrobium has showy flowers and a tolerably perfect nectary; while Corysanthes has conspicuous flowers and sweet juice. In all three, assistance from insects appears to be absolutely necessary. Again, Caladenia, which appears to be fitted for both means of fertilization, has tolerably conspicuous flowers, while Microtis, which is similarly favoured, has the rudiments of a nectary, but the former would seem to be more dependent on insect aid than the latter. In Pterostylis there seems to be nothing to attract insects, as the flowers are green, and, as pointed out by Mr. Cheeseman, do not appear to secrete any nectar, nor do they have any decided scent. Yet in none of the New Zealand orchids are the appliances to secure the desired end so perfect or so complex. In this plant only one species of insect appears adapted to each particular species of the genus. It would be interesting to discover whether this applies to other New Zealand genera. In those genera which are almost, if not altogether, exclusively self-fertilized, no special provision for attracting insects occurs, if we except the handsome perianth of Thelymitra.