Osmunda claytoniana , Z., and O. cinnamomea , Z. 57 
prothallia branch irregularly, or in some cases there seems to 
be a true dichotomy (Fig. 21); but in the latter case one of 
the branches finally grows faster than the other which is sup- 
pressed, and the resultant prothallium does not differ much 
in appearance from the ordinary type. In this species, too, 
filamentous prothallia are common, especially when the young 
prothallia are crowded. These filamentous forms are much 
rarer in O. cinnamomea even when growing very close to- 
gether, and are never developed to the same extent. These 
filamentous forms recall very strongly the similar ones found 
in Trichomanes , and taken in connection with the similarity of 
the sexual organs, suggest a not very remote relationship 
between the Osmundaceae and Hymenophyllaceae. On the 
other hand, some of the more massive branched forms recall 
those of Equisetum . 
Kny 1 and others have called attention to the marked ten- 
dency to multiply by adventitious buds shown by the prothallia 
of the Osmundaceae. These secondary prothallia (Plate IV, 
Fig. 33 //) arise from the margin usually, but may be formed 
from the lower surface. An apical cell is usually early esta- 
blished, and the subsequent growth is essentially the same as 
in the primary ones. As they often form near the base of the 
old prothallia, they may become entirely independent by the 
dying away of the cells of the primary prothallium, and some- 
times whole groups of these secondary prothallia are found 
growing from a single primary one. They grow rapidly after 
they are formed, and produce perfectly normal sexual organs, 
and presumably embryos. 
The chloroplasts, which in the ungerminated spore are small 
and crowded, separate as the cells expand, and increase rapidly 
in size, and by repeated divisions give rise to new ones. They 
are thin flattened plates, lying close to the wall of the cell, 
and from mutual pressure usually somewhat polygonal in 
outline (Fig. 32). As usual, after exposure to light, small 
starch-granules are evident in them. Several times very large 
chloroplasts of peculiar form were seen in prothallia of O. cin- 
1 L. c. p. 7. 
