Bower.—Studies in the Phytogeny of the Filicales. 441 
is seen commonly in the sporangia of the Leptosporangiatae, is so marked 
that it again indicates that Plagiogyria occupies a position distinct from 
other Ferns with a ‘ mixed * sorus; nor is it apparent that the same 
variability holds in any of the Gradatae. It suggests that sort of plasticity 
which might have accompanied the shifting of the point of dehiscence 
from a median to a lateral position—a change which comparison indicates 
to have actually taken place in the phyletic transition from the Simplices to 
the Gradatae and Mixtae. 
If we regard the sporangium of Plagiogyria from the biological point 
of view, it will appear that it is not highly specialized in accordance with 
its requirements. There is no regular sequence of the sporangia in the 
sorus, consequently the oblique position of the annulus is not a feature 
of high moment. The induration shows a considerable interruption, the 
thin-walled region including the stomium ; it extends down to, or even 
sometimes across the insertion of the stalk, so that a condition is arrived at 
which is not unlike that of the Polypodiaceous type; it has, however, the 
mechanical disadvantage in the case of Plagiogyria as compared with these 
that the end of the indurated annulus is not directed straight to the stalk 
itself, but obliquely towards it. The sorus not being a crowded one this 
point is probably immaterial. The retention of the oblique annulus, as 
in the Gleicheniaceae for instance, with only the modification of the dehis¬ 
cence having been swung into a lateral position, is in no way surprising 
when it is remembered that there is only a slight departure here from the 
primitive sorus of the Simplices. 
There has been some difficulty in obtaining germination of the spores; 
the cultures of spores of P. semicordata from Jamaica came on very slowly, 
and prothalli are only sporadic, many spores failing to germinate. This 
may raise some doubt of the identification, though the prothalli observed 
appear in close relation to undoubted sporangia of Plagiogyria , and the 
form and character of the spores from which the individual prothalli arise 
are those above described. The difficulty of identification lies in the fact 
that, in the absence of the highly refractive globules above noted (which 
were seen not to be firmly attached to the mature spore, and seem to dis¬ 
appear on germination), no marked features remain beyond the tetrahedral 
form. Final certainty of identification must be awaited when the prothalli 
have produced young sporophytes. 
The character of the prothalli observed are, in general, those usual 
for Leptosporangiate Ferns, being- commonly symmetrical in form, and 
without any distinctive hairs or glands. The interesting feature is in the 
antheridia, of which the distinctive modes of dehiscence have been pointed 
out by Heim (‘Flora/ 1896, p. 349); the one type characteristic of the 
Osmundaceae, Gleicheniaceae, Lygodium , Hymenophyllaceae, Cyatheaceae, 
and Dicksonieae, shows dehiscence by throwing off a lid-like cell, which 
