THE HOMOSPOROVS LEPTOSPORANGtAT^. 



369 



The Embryo 



To judge from the few rather vague statements made by 

 Rauwenhoft* in regard to the embryo, this more nearly re- 

 sembles the typical leptosporangiate type than it does Osnmnda. 

 The primary root has a large and definite three-sided apical cell, 

 and the divisions in the segments are very regular. 



The Adult Sporophyte 



Poirault ( i ) and Boodle (3) have made a study of the stem 

 of various species of Gleichenia, which differs a good deal from 



Fig. 211. — Gleichenia flabellata. Development of the sporangium; A, B, X300; C, 



X150. (After Bower.) 



that of Osmiinda, and approaches that of the Hymenophyllacese 

 and Schizgeaceae. A single axial bundle traverses the stem, and 

 is separated from the sclerenchymatous cortex by a distinct en- 

 dodermis. Within the latter is a pericycle of several layers 

 of cells, within which is a continuous zone of phloem containing 

 large and small sieve-tubes, and phloem parenchyma. Within 

 the phloem are also secreting cells. The whole central part of 

 the stem, except in G. pectinata, is occupied by bundles of large 

 scalariform tracheids separated by parenchyma (Fig. 210, C). 

 The single bimdle traversing the petiole is much like that of 



