Page:Proceedings of the Royal Society of London Vol 60.djvu/282

256 parable to that of Trichomanes al in which apogamy and apospory co-exist. P rothalli have been found to arise directly from the older fronds of another variety of Scolopendrium.f

An attem pt will now be made to bring the peculiar modification of the life-history cycle of these ferns into relation w ith previously recorded cases of apogamy, and to estim ate its theoretical bearing. A full consideration of these points m ust be deferred until more extended observations have been made.

There seems no reason to doubt the prothallial nature of the cylindrical process : its origin, the character of its cells, the presence of functional sexual organs, the developm ent of rhizoids, and the direct transition to an ordinary flat prothallus apex sometimes m et with, are sufficient grounds for this conclusion. The distinction between its origin as a direct continuation of the prothallus, and the cases in which it arises behind th e apex which has lost its meristem atic character, is not an essential one. Both forms occur in in the latter case the process may be compared with the numerous elevations which appear on the under side of old protballi of Doodia caudata,% and are capable of apogamous development. The formation of such processes by prothalli which have attained a considerable size w ithout having been fertilised, appears to be of not infrequent occurrence, and is usually associated w ith apogamy. It is recorded in Todea pellucida, Garm., T. rivularis, Sieb.,§ and filixfcemina, Bernh,|| and th e w riter has found in Loive, as m any as six apogamous buds, formed from the tips of cylindrical processes, w hich arose from the anterior m argin of a prothallus.

The term cylindrical process^]" has been used to avoid confusion with the middle lobe developed in aborting prothalli of Pteris cretica and Aspidium filix-m as, This, as Le Bary has shown, may be regarded as corresponding to some extent with the first leaf of an apogamous sporopbyte.** A structure oomparable w ith this middle lobe has been found in prothalli of, which had also produced a cylindrical process; usually one or more sporangia were borne upon it.

Tracheides were always present in the tissue beneath sporangia, *§

f Druery, ‘Linn. Soc. Journ,,’ vol. 30, p. 281. J Heim, loc. cit.,p. 340, fig. 12. § Stange, loc. cit, 1| Druery, ‘ Gard. Chron.,’ November 10, 1895. It is impossible to determine whether the structure to which Wigand (‘Bot. Zeit.,’ 1849, p. 106) applied this name, and which he inclined to consider as a rudimentary axis, was of the same nature or was a true middle lobe, but the latter appears the more probable conclusion.
 * Bower, ‘ Annals of Botany,’ xol. X, p. 300.
 * Loc. cit., p. 464.