590 FILICALES 
The form of the parent cells of the sporangia is not constant ; commonly 
the cell has a square base, and the first segment-wall passes obliquely to 
the basal wall (Fig. 329 a and c), the next segment-wall being inserted 
obliquely on the first: the result is from the outset a sporangium with a 
short massive stalk, as shown in Fig. 329 p. In other cases the parent 
cell is more wedge-shaped, and the first segment-wall cuts an oblique lateral 
wall (Fig. 329 B): thus the segmentation in Zhyrsopferis wavers between 
two types—the one characteristic of larger, the other of smaller spore-output. 
The further segmentation of the sporangial head follows the type usual for 
Leptosporangiate Ferns. Very soon, however, the sporangium takes an 
Thyrsopteris elegans, Kze. A=longitudinal section through the young sorus, showing 
fiefoa ar We distal Uigieok. Coty yous mOTMEen Scare ILE Hie acta, 
D=a sporangium with tapetum and sporogenous group shaded. Z, /=mature 
sporangia. A-DX2c0, E, # X50. 
unsymmetrical form, the more strongly growing side being that directed 
towards the apex of the receptacle (Fig. 329 D): the oblique annulus, which 
in this genus presents peculiar characters, makes its appearance early, and 
occupies a position comparable to that in Gleschenta: the orientation of the 
sporangia is thus on the Gleicheniaceous type, which, when repeated and 
associated with lateral dehiscence, offers the advantages for spore-dissemi- 
nation noted in the Hymenophyllaceae, and effective in other Gradatae. 
The central cell undergoes the usual segmentation to form a tapetum of 
the usual type, and 12 to 16 spore-mother-cells. From countings of the 
spores it has been concluded that the typical number for each sporan- 
gium is from 48 to 64. 
The sporangia when mature are of large size and rather peculiar form: 
seen from without they present some rather unusual features. Fig. 329 F 
shows one presenting its central face: the annulus, starting from the base, 
