OUR NATIVE FLORA.

Auckland Star, Volume LV, Issue 116, 17 May 1924, Page 27

OUR NATIVE FLORA.

A BOTANIST'S JOTTINGS.' A WINTER BLOSSOM. (MARGUERITE W. CROOKES, M.A.) At a time when the bush is almost flowerlos?, when the winter sunshine falls upon a world of green, lit only by ornngc or scarlet berries, it is a surprise as well as a delight suddenly to find springing from branch or cliff sprays of white flowers as delicate, fragrant and ethereal as anything with which the summer can provide us. For the Raupeka (Earina Suaveolens) may justly claim to be one of the most exquisite of our New Zealand blooms. It is an orchid, and like all orchids, has a flower which is strange and interesting as well as beautiful, for .this family contains some of the most amazing and complicated flowers in the world. Even our little Raupeka, which is a comparatively simple orchid turns out on examination to be an extremely ingenious arrangement. An Insect Helper. Now we all know that flowers exist for the purpose of seed making. But before seed making can take place, the flower must be pollinated. That is to say, some of the yellow dust called pollen must be transferred from a particular part of one plant to a particular part of another. (Sometin.es a flower is pollinated by its own pollen, but this is not usual, pollen from another flower generally being necessary to produce healthy seed.) The pollen is most frequently transferred from flower to flower by insects or the wind. Now, let us consider the charming little cream and yellow flower of Raupeka and see how it solves the pollination problem. It is impossible to give full details because the flower is somewhat complicated, but what happens is something like this. An insect visitor alights upon a protruding petal known as the lip, and ornamented with two bright yellow spots. Having settled itself it proceeds to investigate matters by poking ■ its head down into the heart of the flower. Here it comes upon some pleasant tasting liquid which the flower has provided for it. But the flower does not feed it for nothing. Oh, no! That nice little meal is "for service rendered," and the flower takes very good care to see that the service is performed, as we shall see. Having finished its meal, the insect proceeds to "back out" of the flower, and in so doing it strikes its head against two small projections. Now in an ordinary way nothing might happen, but the plant has all eady taken the precaution of Bmearing the insect with a sticky material so that as soon as it comes into contact with these projections they become securely "gummed on" to it. Now these projections are nothing less than the tiny stalks of balls of pollen, which are thus drawn away by the insect. And the flower contrives by a very clever little mechanism that these Little pollen balls shall stick on just that part of the visitors' back which will bring them into contact with the right part of another flower, thus fertilising it. A Living Reservoir. Turning now to the roots of Raupeka, we find them no less interesting than the flowers, since they show such interesting adaptations to its somewhat elevated situation. Now light is essential to green plants, and since the floor of the bush is extremely shady and Raupeka is rather small, it obviates the difficulty of a light shortage by leaving the ground and perching in some well-lit crevice on branch or cliff. But having solved the light difficulty, our Raupeka is now confronted with the food and water problem. In its enterprising search for sunshine it has abandoned the abundant supplies of nourishment which would have been ready to hand on the ground below. Well, Raupeka overcomes all these ap- N parently formidable difficulties, in the first place by collecting every available scrap of food or drop of water that comes its way, and, in the second place, by very carefully conserving and storing its supplies. In the nooks and crevices where it perches there is always a' certain amount of decaying vegetable matter to begin with, and as it develops Raupeka sends forth a considerable quantity of roots in whose meshes any additional scrap of decaying moss or lichen that falls upon it may be retained to augment the existing food supply. But all this would be useless to Raupeka were it not for the remarkable manner in which it has modified its roots to make a little go a long way. It has two kinds of roots. (1) "Ordinary" roots which serve to clamp it firmly into its position on rock or tree, (2) absorbing roots which are snecially adapted to secure anything and everything practicable in the way of food. Now the roots of plants living on the ground do not absorb water all over their surfaces but only through special hairs situated near the root tip. Supplied only with roots of this type Raupeka would certainly starve. So it proceeds to alter some of its roots so that they can absorb water all over their surfaces. If we examined them under the microscope we should cc that for this purpose each root is provided .with a band of spongy tissue consisting of about five layers of cells, completely enveloping the root. From the outer layer of this spongy tissue" project numerous hairs that help to absorb moisture. This spongy tissue consists of dead cells, which are mostly empty, but here and there among them are cells with specially thickened walls which servo to give" rigidity to the tissue, and may also act as water vapour condensers. It will be seen at once that this spongy tissue is excellently adapted to soak up with great rapidity any moisture that falls upon the surface of the roots. But, the reader may think, suppose a shower of rain were followed by strong sunshine, would not the water very speedily he dried out of the absorbing tissue? If it remained in these outer layers it certainly would, but it is immediately transferred to the> inner part of the foot. Just below the spongy tissue there is a layer of cells that most effectively protects the interior of the root from loss of moisture because it is impervious to water. However, at certain intervals in this layer are cells that admit the passage of liquid, and it is through these that any moisture absorbed by the spongy tissue pusses through into the interior. On the top of each of these cells there is a very curious arrangement, which consists of a cell so filled with strands of a hard material as to be almost solid and containing only a small passage for water.

•It is believed by some scientists that these cells act ss water vapour condensers. However that may be, such cells would certainly act as a most efficient vegetable stopper in case the plant should desire to cut off communications between the inner part its roots aud its absorbing tissue. So we see that once water is absorbed and passed to the jiiner part of the root it cannot be "dried out"' again, since it is protected hy a layer of tells that is always partly, and may become completely, waterproof. Additional Precautions. V c find then that these roots absorb the/naximum amount of water in the minimum amount of time, and while bringing about the entry of all available water into the tissue have a very effective method of preventing it getting out again. But all these contrivances would be of little use to Raupeka if too much water was evaporated through its leaves. Xow if we compare the leaves of Raupeka with those of orchids living on the ground, we find that the leaves of the former are much smaller and narrower and present less surface to the sun. They are also protected from harm by a strong outer covering, and we notice they are thick and leathery to feel and not easily dried up. Consequently they do not readily lose their water supply through evaporation. Provided with so many ingenious contrivances for its comfort and convenience it is small wonder that Raupeka is able to maintain life successfully under apparently unpromising circumstances, and year by year send forth its exquisite sprays to delight us. Fortunately this dainty blossom is not confined to the north, but is found in both islands. Moreover, it is not tbe only one of its family., but has several charming relatives very similar to it?elf. one of which flowers in the. spring and another in the autumn. But we owe Ruapeka a special debc of gratitude in that it has beautified for us the most I flowevlcss of the seasons.