i73 
A zolla filiculoides , Lam . 
two cells giving rise directly to the egg and the canal-cells, 
the upper to the neck, no basal cell being formed. In this it 
agrees with the other heterosporous Pteridophytes. 
Up to the time that the first division in the archegonium is 
completed, the whole prothallium has increased somewhat in 
size, but this has been entirely at the expense of the spore- 
cavity, and the exospore has remained intact. The central cell 
of the archegonium is separated by a single layer of cells only, 
from the spore-cavity. The young prothallium at this stage 
(Fig. 47) recalls quite strongly that of Pilularia at a similar 
stage, but also agrees closely with Prantl's account of Salvinia. 
Berggren’s figures 1 of prothallia of A. caroliniana , at a stage 
presumably about the same, are too diagrammatic to allow of 
a satisfactory comparison. They represent the prothallium as 
composed of perfectly uniform cells arranged in rows con- 
verging at the top, where a very small archegonium mother- 
cell is shown. The whole is totally different from anything 
observed in A . filiculoides. 
Shortly after the first division in the archegonium, a rapid 
increase takes place in the size of all the cells of the pro- 
thallium, by which it expands and ruptures the exospore, 
which breaks open at the top into three lobes corresponding to 
the three converging lines that mark it at that point. 
The most remarkable difference observed between A zolla 
and the other Hydropterideae is the history of the lower of the 
two nuclei resulting from the division of the primary nucleus 
of the macrospore. In the Marsiliaceae this remains un- 
divided, and in the later stages seems to become more or less 
completely disorganized. In A zolla, however, where it is quite 
equal in size to the nucleus of the prothallium mother-cell, it 
undergoes repeated division, the resulting nuclei remaining 
imbedded in the protoplasm of the upper part of the spore- 
cavity, in close proximity to the cells of the under side of the 
prothallium (Fig. 47 n). While the albuminous granules 
become larger in the lower part of the cavity, the upper 
nucleated protoplasm loses them almost entirely, and in 
1 loc. cit. Figs. 7 and 9. 
