CYATHEACEAE 



[CH. 



at first distally, while later others are formed lower down. There is in fact 

 a basipetal succession, but it is not long continued, the number of sporangia 

 in the sorus being small in this species. There is no sign of an indusium at 

 the base of the receptacle. All the appearances are as in Lophosoria, or in 

 the advanced species of Gleichenia, excepting in the number and the basipetal 

 succession of the relatively small sporangia. The origin of the receptacle of 

 Cyathea differs in no essential point from that oi Alsophila, but here a basal 

 indusium appears as a rather massive ring before the first sporangia are 

 formed. These again arise in basipetal succession, and in the instance shown 

 in Fig. 565 the oldest sporangium is seen to have been developed from the 

 extreme tip of the receptacle. The longest successions of sporangia are seen 

 in certain species of Heinitelia, but none of the Cyatheaceae attain to such 

 a development of the receptacle as that seen in Trichomanes. 



\\ 



Fig. 565. Cyathea dealhata Sw. The upper 

 figure shows a very young sorus, with recep- 

 tacle and indusium already indicated. The 

 lowershowsthe indusium (?) more advanced, 

 and the sporangia {s, s) arising in basipetal 

 succession, ( x 200.) 



Fig. 566. Segmentation of the sporangia 

 of Heinitelia capensis; five of the 

 sporangia show the two-sided sporo- 

 genous cell (shaded) ; centrally is one 

 where the 4-rowed stalk is traversed : 

 //, h are hairs. ( x 200.) 



The segmentation of the sporangium presents features of interest. The 

 parent cell frequently has a wedge-shaped base, and the first segment-wall 

 is inserted on one of the oblique lateral walls. This type is thus intermediate 

 between that of the Simplices and that seen in the smaller sporangia of the 

 Leptosporangiates. But the further segmentation is by alternate cleavages 

 in two rows, which are succeeded by the formation of a cap-cell. An 

 examination of the sporangia in Figs. 564, 565, shows this, but the structure 

 is best appreciated in sections tangential to the surface of the receptacle, 

 which cut the individual sporangia transversely (Fig. 566). From these it 

 appears that the internal cell has the shape of a biconvex lens, not of a 

 three-sided pyramid as in most Leptosporangiate Ferns. A natural con- 

 sequence of this segmentation is that the stalk is composed of four rows 

 of cells, each of the segmental cells having been divided again by a radial wall. 



