The hairy tuft attached to the base of seeds in
Salix and
Populus has long been believed to arise from the funicle (
cf. KERNER, Pflanzenleben; LE MAOUT et DECAISNE, Traité générale de Botanique; LEUNIS, Synopsis; etc.). Only comparatively recently TOEPFFER1) described that the hairs arise from a part of placenta which comes off at maturity of capsule. In the third edition of GOEBEL'S Organographie2) one finds a fairly detailed description of the hairy tuft. He explains that ovule of
Salix possesses well developed funicle which is covered, after fertilization, with hairs that become longer than the seed itself. He also notices that similar hairs also arise from the placenta which becomes detached when the fruit is ripe.
The present writer had occasion of examining a number of young as well as fertilized ovules in certain species of
Salix, in connection with studies on other features of flower and fruit of this genus. The result was then read before a meeting of the Botanical Society, London, in 1911, but so far it has not been published in print. Later, more material was gathered, including the allied genus
Toisusu. The present paper deals with the nature and development of the hairs in the above, mentioned two genera. To make things as simple and clear as possible, the writer proposes to put down here the more important points only, as follows:
1. The ovules in both
Salix and
Toisusu have no discernible funicle. That designated as such by GOEBEL1) is nothing more than a part of placenta, and is not real funicle at all.
2. The epidermal cells of placenta in these two genera possess in early stages dense protoplasmic contents, and can readily be distinguished in shape and nature from those of the ovary-wall.
3. Those cells show sign of elongating into a long hair before fertilization.
4. Elongation starts first at the very bottom of the ovary, and gradually extends upwards and reaches far beyond the highest level at which ovules are borne.
5. At the maturity of capsule, and when it splits into two valves that roll back, the hairy tuft becomes then, together with part of placenta, detached from the wall, and is blown about by wind, thereby carrying seeds together. The shrivelled piece of placenta has often been mistaken for funicle, e.g. GOEBEL, l.c. fig. 2082 II, F.
6. The hairs are developed to some extent even in an abortive ovary, and in the normal cases, always before the fertilization, stimulus other than fecundation seems to make the embryonic cells of epidermis to start.
7. The hairs do not always carry seeds, this being particularly well evidenced in
Toisusu; no teleological meaning should therefore be ascribed to them, as to their having aim from the outset to be an apparatus of dispersal.
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