Osmunda claytoniana , Z., and O. cmnamomea , Z. 65 
the opercular cells and method of dehiscence. The sperma- 
tozoids closely resemble those of Equisetum both in form and 
movement ; and in the smaller number of coils suggest an 
approach to the simpler form found in the liverworts and most 
mosses. 
The Archegonium. 
The prothallia that bear archegonia are larger than the 
males and always heart-shaped. They are more elongated, 
especially at the base, than is common in Polypodiaceae. 
Almost from the first, the midrib, several cells in thickness, is 
present, passing abruptly into the wings of the prothallium, 
which are but one cell thick. As we have seen, growth is at 
first due to a single triangular apical cell, which is replaced by 
a four-sided one, as in Pellia , and then, in most cases at least, 
by several similar initials, as in other ferns. These large 
prothallia produce antheridia first, but in smaller numbers 
than the strictly male plants : nevertheless new ones appear 
after the formation of archegonia begins, and self-fertilization 
must frequently occur. 
The midrib, which is at first only four or five cells thick, 
becomes later three or four times as thick, and in O. clay- 
toniana very much broader after the archegonia begin to form. 
In this species, too, the formation of lateral lobes in the sinus 
at the front of the prothallium is less marked than in the 
other species, although the young prothallium is much more 
irregular in outline. 
Owing to unfavourable circumstances, the archegonia were 
late in developing, and I cannot say how soon they are formed 
ordinarily. The first full-grown archegonia were not formed in 
my cultures until more than four months after the spores 
germinated, but from that time they continued to form as 
long as the plants were kept. During the late autumn and 
winter growth was slow, but about the end of January it 
began again vigorously and so continued. 
As in O. regalis \ the archegonia do not cover the whole 
1 Kny, 1 . c. p. 10. 
F 
