378 



MOSSES AND FERNS 



CHAP. 



closely with those of the other Leptosporangiatae. The coty- 

 ledon is simple with a single median vein, and a root is present 

 in all species yet examined. 



The Mature Sporophyte 



Prantl ( i ) has given a very complete account of the struc- 

 ture of the mature sporophyte, and Bower ( 1 1 ) has added to 

 this by a careful study of the meristems of the different organs. 

 From the investigations of the latter it seems that here, as in 

 nearly all other Ferns, the stem apex has the usual three-sided 



Fig. 219. — Pinna of the leaf of Hymenophyllum recurvum, X3; B, part of rhizome (r) 

 and leaf of Trichomanes parvulum, X3; C, pinna of the leaf of Trichomanes 

 cyrtotheca, X3; D i, trumpet-shaped indusium of the same, X4; 2, section of the 

 indusium (td) with the central sorus, X 5 ; ^, the sorus. 



initial cell, but only a small part of the segments give rise to 

 leaves, which are arranged in two ranks. 



The stem in all investigated Hymenophyllacese is mono- 

 stelic, and one leaf-trace passes to each leaf. The cortex is 

 usually largely made up of sclerenchyma, especially the inner 

 cortex. In Hymenophyllum recurvum (Fig. 220), the axial 

 vascular bundle is strictly concentric. Occupying the centre 

 is a curved band of tracheary tissue, the small central tracheids 

 being the protoxylem. Around the xylem is a continuous zone 



