56 Campbell. — On the Prothallium and Embryo of 
elongation of the cell, or, as is commonly the case in the 
Polypodiaceae, from a papilla which is cut off from the 
mother-cell. Kny does not seem to have seen this latter 
form in O. regalis , but it is by no means rare in both species 
considered here. In O. cinnamomea the walls of the root-hair 
become dark-brown, as in O. regalis , but in O. claytoniana this 
is much less marked. 
As the prothallia become older, their general appearance 
in the two species becomes quite different. In O. claytoniana 
the margins are more irregular (Fig. 22), and the colour much 
lighter, being sometimes almost yellowish-green, whereas in 
O. cinnamomea the colour is dark-green, approaching that of 
AnthoceroSy for example. This dark colour, together with the 
smoother margin, and dark-brown root-hairs, gives the pro- 
thallium quite a different appearance from that of the former 
species. 
As the prothallia grow older, the midrib becomes more 
conspicuous and projects strongly from the lower surface. In 
O. cinnamomea , even at maturity, it does not broaden much, 
even where the archegonia are borne ; but in O. claytoniana it 
suddenly becomes much broader and thicker when the arche- 
gonia begin to form, and projects very strongly, just back of 
the growing-point, as a hemispherical cushion, very like that 
found in the Marattiaceae and older prothallia of the Poly- 
podiaceae, and in this respect, as well as the form of the apical 
cells, seems to approach the latter. 
In studying the development of the prothallium in both 
species, numerous irregularities were noted. Frequently, as 
in other Osmundaceae, a cell-mass is formed. as the first result 
of germination (Figs. 15, 19), but this condition is only tem- 
porary, a single apical cell being early formed which then 
gives rise to a cell-surface as in the usual forms. Occasionally 
no root-hair is formed at first (Fig. 8) ; or prothallia may be 
met with composed of two parallel rows of cells without any 
definite apical cell (Fig. 18), recalling strongly a certain type 
found in Equisetum. 
Not infrequently, especially in O. claytoniana , the young 
