164 
Notes. 
cylindrical 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 prothallus-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 merismatic 
character, is not an essential one. Both forms occur in Lastraea 
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 caudata *, and are capable of apogamous development. 
The formation of such processes by prothalli which have attained 
a considerable size without having been fertilized, appears to be of 
not infrequent occurrence, and is usually associated with apogamy. 
It is recorded in Todea pellucida , Carm., T. rivularis , Sieb. 2 , and 
Athyrium filix-foemina , Bernh. 3 , 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 4 has been used to avoid confusion 
with the middle lobe developed in aborting prothalli of Pteris 
cretica and Aspidium filix-mas. This, as De Bary has shown, may be 
regarded as corresponding to some extent with the first leaf of an 
apogamous sporophyte 5 . A structure comparable with this middle 
lobe has been found in prothalli of Lastraea 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, 
and the question arises whether their occurrence is to be regarded as 
of morphological significance. They have been found in the pro- 
thalli of a number of species of Ferns, and, in every case investigated, 
were associated with apogamy. In the case of Pteris cretica , the 
differentiation of the tracheides in the prothallus precedes the origin 
1 Heim, loc. cit., p. 340, Fig. 12. 
2 Stange, loc. cit. 
3 Druery, Gard. Chron., November 10, 1895. 
4 It is impossible to determine whether the structure to which Wig and (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. 
0 Loc. cit., p. 464. 
