Osmundo claytoniana, L., and O. cinnamomea , L. 8 1 
cells in immediate contact with the prothallium-cells some- 
times grow out into short, root-like processes, that recall the 
similar organs in the foot of the sporogonium of the Antho- 
ceroteae, and of course serve the same purpose. On account 
of the great development of the foot, the embryo grows for a 
long time at the expense of the prothallium, and is late in 
breaking through the calyptra. 
When the embryo is about to break through the calyptra, 
the first tracheary tissue can be detected, first forming in the 
axis of the embryo and proceeding from this point into the 
organs of the embryo. The tracheids are short and marked 
with close annular or reticulate thickening. 
The calyptra is very large (Fig. 96 cal). After the arche- 
gonium is fertilized, active growth begins in the cells of the 
venter, which keeps pace with the growth of the embryo and 
forms a covering entirely around it, two cells thick in most 
places, but sometimes more. It is not until the embryo is far 
advanced that this is finally ruptured. The cotyledon usually 
breaks through first, and then the root, which being usually 
vertical soon penetrates the ground and fastens the young 
plant to it. 
Both the very large foot and the very large calyptra recall 
strongly the Bryophytes in which the sporophyte prominently 
derives part of its nourishment from the oophyte. 
Soon after an archegonium is fertilized, the regular apical 
growth of the prothallium ceases, and soon none but vertical 
walls are formed in the apical cells, so that the forward part 
of the prothallium, like the rest of the margin, is but one cell 
in thickness. Finally all growth ceases and the prothallium 
dies. 
Frequently more than one archegonium is fertilized as in 
the Gleicheniaceae 1 , but as a rule only one embryo develops, 
although it is not at all uncommon to find several archegonia 
where the egg has evidently been fertilized, as is shown by its 
enlargement and investment with a cell-wall. Only one case 
was met with when two embryos were present, but one of 
1 Rauwenhoff, 1 . c. p. 53. 
G 
