NATURE NOTES

Evening Post, Volume CXIII, Issue 48, 26 February 1927, Page 15

NATURE NOTES

AN INTERESTING^ ORCHID ,r THE RUAPEKA (By b. h. d. stidojp.h,)::.: r^i:: At the present time, au autumW flowering orchid, the ruapeka, is justt coming into fiotyer in the writer's gar-" den. _ Tliis species is one of the most exquisite of native orchids—not only! is the flower strange and interesting, m common with all orchids, ■ but tha sprays of delicate white flowerßare deliciously fragrant. Pollen is usually; transferred from flower to flower/ by. insects or the wind. The flower of the ruapeka is somewhat complicated, but its method of pollination takes placa m a strange manner. An insect visitor alights upon a protruding petal known as the lip, which is ornamented with two bright yellow spots. It thew investigates matters and pokes its head into the heart of the flower, where, some pleasant-tasting liquid rewards us industry. But for this offering of tood some service is expected from the visitor. The insect proceeds to back out, but not before it has been smeared with a sticky material, so that" as soon as it comes into contact with two small projections, balls of pollen, which, block the exit, the pollen is transfer-' red to the visitor's back, which will bring it into contact with the correct part of another flower. In this way is fertilisation brought - about. ■ . '--:-v:' The ruapeka grows as "an- epipiytef perhaps on some finest tree, "and the roots show ingenious adaptations to its elevated situation. In a charming little book on New Zealand plants written oy Miss Marguerite "Oookes” , •' lnc oue of many interesting chapters'on. the biological aspects of native plants, adaptations of the roots are described. "New light is essential to green plants, and since the floor of the bush is extremely shady and iuapeka is rather small, it obviates the difficulty of a light shortage by leaving the ground and perching iv some well-lit crevice on branch or cliff," writes Miss Grookes. "But having solved the light difficulty,;. our "rua-" peka is now confronted with the food, and water problem. '. .. . Well, ruapeka overcomes all these apparently; formidable difficulties, "in the firs'fc 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. iiooks and crevices where "it perches there is always a certain amount- of decaying vegetable matter to begin with, and. as it develops ruapeka sends forthi:a con-.' siderable 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 for ruapeka 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 specially adapted 'to secure anything and everything practicable in the way of food. Now the.roots of plants living in 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, ruapeka would certainly starve. So it proceeds to alter some of its roots so that they can absorb water all over their surfaces. . . ■-."■ ■ ...

If these roots are examined" it Will be seen, that,each one; is provided wither a band, of spongy tissue' c~onsisting~"of about Svq. layers of cellsr completely ■' enveloping the' rob'f.". Numerous hairs that, help to absorb moisture.project from the outer layer of this spongy tissue, which consists of dead cells, which are mostly empty, but here and there among them are cellsi with specially thickened walls. These walla serve to give rigidity to the tissue, and may also act as water condensers. This spongy tissue is excellently adapted to soak up with great rapidity any moisture that falls upon .the surface of the roots. Just below the - spongy tissue there is a layer of. cells, that most effectively protect the interior of the . root from loss of moisture,; as it is am-'----pervious to water. However, at intervals in this layer are cells••!that admit ' the passage of liquid, and it is through these cells that any moisture absorbed by the spongy tissue passes into the ' interior. The roots absorb the maximum amount of water in the minimum , amount of time and have a very effective arrangement of preventing the water from escaping again. These contrivances, however, would be of little'" use if too much water was revaporated";through its leaves. The leaves of rua-/': peks. are small and protected, from-harn*"-.-.' by a; strong outer covering.",: Conse-'■■'; quently this orchid is provided against^ loss of water, supply: through' evapbra^:'■• tion. All New Zealand naturalists should possess a copy of Miss Crookes'r ' charming publication.