PTERIDOPHYTES 
ferns, and that Salviniaceae have the transverse wall of the older 
eusporangiate Marattiaceae. 
Conclusions. It is evident that the water ferns are a very specialized 
aquatic group, probably derived from the leptosporangiate ferns. More- 
over, the features of the sporangium, in development and output, in- 
dicate an origin from one of the higher leptosporangiate families. The 
FIGS. 416, 417. Female gametophyte of Marsilea: 416, the tissue protruding from 
the heavy megaspore wall developing a single large archegonium; the top of the large 
nutritive cell with its single nucleus seen; 417, the mature archegonium. After 
CAMPBELL. 
annulus characters, which might have determined the point, are lacking. 
It is interesting if heterospory has developed in these aquatic conditions ; 
and it is noteworthy that the development of the female gametophyte is 
very different from that of Selaginella and Isoetes, which resemble 
gymnosperms in this regard. The fern connections of Marsileaceae are 
clearer than those of Salviniaceae, which in habit are further removed 
from the terrestrial leptosporangiates. 
