CYATHEAE 603 
is cup-like, and may form a complete investment for the sorus while young. 
The disposition of the sori is fundamentally as in G/leichenta, in a single 
series on either side of the midrib of the pinnule; but the regularity of 
the series is liable to be disturbed according to the mode of growth of 
the leaf. Moreover, the identity of the sorus is not always maintained, 
fissions (or fusions) being frequently seen. 
The development of the sorus has been followed in A. atrovirens: an 
early condition of it is shown in Fig. 334 a, in which the sporangia near 
the apex of the receptacle have the cap-cell already formed, while in the 
lower sporangia on either side it is not yet cut off. ‘The succession is 
thus basipetal, though not markedly so, since their number is not very 
large in this species. The sporangia are from the first more robust than 
those of Cyathea, but less so than those 
of Gleichenia, to which they correspond 
in the oblique annulus, and in their 
position in the sorus: moreover, the 
first segmentations take a middle place: 
the parent cell of the sporangium has 
frequently a wedge-shaped base, and 
the first. segmentation-wall cuts one of 
its oblique lateral walls: this type is 
thus intermediate between that of the 
more robust Simplices and that of the 
smaller sporangia of the Polypodiaceae. 
In point of its convex form and actual 
size the sporangium of A. atrovirens : ; 
does not differ widely from that of ie ei oie oa ee tate indica: 
Gleichenia dichotoma, but the stomium a Be en ceoee 
3 ci : . Mature; 4=a transverse section of a sporangial 
is lateral as against the median dehi- stalk. X50. 
scence of Gleichenia : still it is obvious 
that the cells of the stomium form part of the very regular series of the 
annulus (Fig. 334C). The regularity of the orientation is according to the 
type of Glechenia in the basal part of the sorus, but it is not strictly 
maintained by the sporangia at the apex of the receptacle: in this also 
Alsophila corresponds to Gi. dichotoma. The typical number of spores 
per sporangium appears to be 64. 
It is thus seen that Adsophi/a shows certain points of interest for 
comparison with Gleichenia: notwithstanding the difference of habit it 
corresponds in the position of the sorus and in the absence of the indusium, 
while the number of the sporangia in the sorus in A. atrovirens is not 
greatly in excess of that in Géeichenia dichotoma, There is also some 
similarity in the form of the sporangium with its oblique annulus, and in the 
orientation of the sporangia, at least in the lower part of the sorus, though 
in both there is irregularity towards the apex of the receptacle. But there are 
important differences in the position of dehiscence and in the number 
Fic. 334. 
