256 Mr. W. H. Lang. Preliminary Statement on the 



parable to that of Trichomanes alatum* in which apogamy and 

 apospory co-exist. Prothalli have been found to arise directly from 

 the older fronds of another variety of Scolopendrium.'f 



An attempt will now be made to bring the peculiar modification of 

 the life-history cycle of these ferns into relation with previously 

 recorded cases of apogamy, and to estimate its theoretical bearing. 

 A full consideration of these points must be deferred until more 

 extended observations have been made. 



There seems no reason to doubt the prothallial nature of the cylin- 

 drical process : its origin, the character of its cells, the presence of 

 functional sexual organs, the development of rhizoids, and the direct 

 transition to an ordinary flat prothallns apex sometimes met 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 the apex which has lost its meristematic cha- 

 racter, is not an essential one. Both forms occur in Lastrcea dilatata ; 

 in the latter case the process may be compared with the numerous 

 elevations which appear on the under side of old prothalli of Doodia 

 caudala,$ and are capable of apogamous development. The forma- 

 tion of such processes by prothalli which have attained a considerable 

 size without having been fertilised, appears to be of not infrequent 

 occurrence, and is usually associated with apogamy. It is recorded 

 in Todea pellucida, Carm., T. rivularis, Sieb.^ and Athyrium filix- 

 fcemina, B&rnh.,\\ and the writer has found in Aspidium frondosum, 

 Lowe, as many as six apogamous buds, formed from the tips of 

 cylindrical processes, which arose from the anterior margin 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 De Bary has shown, may be 

 regarded as corresponding to some extent with the first leaf of an 

 apogamous sporophyte.** A structure comparable with this middle 

 lobe has been found in prothalli of Lastrcea dilatata, 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, 



* Bower, 'Annals of Botany,' rol. 1, p. 300. 



f Druery, 'Linn. Soc. Jouru.,' vol. 30, p 281. 



J Heim, loc. cit., p. 340, fig. 12. 



Stange, loc. cit. 



|| 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 tho same nature or was a true middle lobe, but the latter 

 appears the more probable conclusion. 



** Loc. cit., p. 464. 



