370 



MOSSES AND FERNS 



CHAP. 



Osmunda, and the lamina of the leaf does not show any peculi- 

 arities. In G. pectinata (Boodle (3) ) , the stele is a hollow cyl- 

 inder with both internal and external phloem and endodermis 

 (Fig. 210, B). 



The Sporangium 



The development of the sporangium has been studied by 

 Bower (19). The young receptacle begins to develop while 

 the leaf is still tightly coiled. From the margin of the circular 

 receptacle, and in some cases also from its upper surface, the 



r 



FIG. 212. A, Pinnule of Gleichenia dichotoma, showing the position of the sori (s), 

 X4J B, ventral; C, dorsal view of the ripe sporangium, X8s. 



young sporangia arise as small conical outgrowths. Each spo- 

 rangial outgrowth undergoes a series of regular segmentations 

 resulting in a central, nearly tetrahedral, sporangial cell, from 

 which successive segments are cut off which give rise to the 

 short, massive stalk of the sporangium. Finally a periclinal 

 wall is formed resulting in the archesporium. The further de- 

 velopment is much like that of Osmunda, except that the inner of 

 the two layers of tapetal cells become very large and their nuclei 



