590 



FILICALKS 



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 D. 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 Thyrsopteris 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 



A 



FIG. 329. 



Thyrsopteris elegans, Kze. A = longitudinal section through the young sorus, slum in,; 

 the two-lipped indusium /, /', and sporangia s, s, seated on the receptacle, the oldest 

 being at the distal limit of it. C = t\vo young sporangia. Z> =one rather more advanced. 

 Z> = a sporangium with tapetum and sporogenous group shaded. E, /~=mature 

 sporangia. A-DXzoo. 



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 Glcic/icnia : 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 sixe 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, 



