POLYPODIUM. 
81 
nately branch the veins which ramify in the lobes ; these 
veins, in average specimens, are pinnately branched, with 
a simple venule directed towards each marginal tooth. 
The sori are sometimes produced only on the lowest 
anterior venule of each lobe, and they then form a series 
on each side the midvein ; but sometimes more of the 
venules are fertile, and the sori then range in short lines 
near the margin of the lobes. 
The very distinct and constant variety called flexile, the 
Pseudathyrium flexile of Newman, has so peculiar an 
aspect, that it is scarcely to be wondered it was thought 
a distinct species. It differs in its lax spreading habit, 
narrow gracely-curving fronds, and short deflexed pinnae, 
with fewer and smaller pinnules. The cultivated plants, 
which are very constant in character, generally produce 
almost stalkless fronds, and these often bear their sori 
abundantly at the base, but scarcely, if at all, on the upper 
parts. These latter marks—the almost sessile fronds, and 
the usually basal sori—disappear in some instances, both 
in the wild and cultivated specimens. An imperfect indu- 
sium has been observed, on some of the sori, in the plant 
under culture, but this occurs only on the least perfect 
sori, and appears to be rather an abnormal development of 
a 
