242 Campbell ’ — Contributions to the 
others are produced ; but in I. echinospora (and it is not un* 
likely that further investigation will show that it is true for 
/. lacustris as well), even before the first archegonium is com- 
plete, two others begin to develop, and reach maturity shortly 
after the first, whether it is fertilized or not. In case these all 
fail to be fecundated a small number (probably never more 
than five or six) may be formed subsequently; but so far as 
my observations go, the production of archegonia on the old, 
unfecundated prothallium, is very limited, as is the growth of 
the prothallium itself. In no instance was the formation of 
chlorophyll noticed, and only in the rarest instances were 
root-hairs developed from the superficial cells, so that the 
prothallium is entirely dependent upon the food-materials 
contained in the spore for its growth, and when these are 
exhausted must necessarily perish. As the prothallium be- 
comes older, the cell-walls become firmer, and more evident 
on account of the absorption of the food-materials in the cells, 
which for this reason become more transparent. 
In regard to the development of the female prothallium, 
Isoetes stands alone among pteridophytes so far as we know 
at present, although it is possible that an investigation of the 
earlier stages of the prothallium of Selaginella may show 
analogies ; but the fact that the true prothallium of the latter 
is separated by a membrane from the lower part of the spore 
would point rather to a formation by true cell-division, as in 
Marsilia 1 and Pilularia 2 . The oophyte of all other hetero- 
sporous pteridophytes is capable to some extent of inde- 
pendent growth, and this is especially true of the Filicineae, 
in which it develops chlorophyll, and may increase very 
considerably in size, provided the archegonia are not fertilized. 
Indeed the development of the oophyte of Isoetes resembles 
much more nearly that of the gymnosperms, or the endosperm 
of the angiosperms, than it does the prothallium of any pteri- 
dophyte, and in this respect must be regarded as the nearest 
approach to the former among the pteridophytes. 
1 Loc. cit. 
2 Loc. cit. 
