270 MOSSES AND FERNS chap. 



The cells immediately adjoining the sporogenous tissue divide 

 into tabular cells, some of which contribute to the tapetum, 

 which is to some extent, at least, derived from the outer cells of 

 the sporogenous complex, as in Ophioglossum. (See also 

 Goebel (22) p. 758). Th^ sporangium shortly before the 

 isolation of the spore mother cells (Fig. 148 C) is a nearly glob- 

 ular body with a thick, very short stalk. The central part of the 

 upper portion is occupied by the sporogenous tissue surrounded 

 by a massive wall of several layers of cells. The central cells, 

 as usual, have larger nuclei, and more granular contents than the 

 outer ones. The stages between this and the ripe sporangium 

 were not seen, so that it cannot be stated positively whether all 

 the cells of the definitive sporogenous tissue (which seems 

 probable) or only a part of them, as in Ophioglossum, develop 

 spores. The wall of the ripe sporangium has 4-6 layers of cells, 

 and sometimes the place of dehiscence is indicated, as in Ophio- 

 glossum, by two rows of smaller cells (Fig. 148, C). 



The stalk is traversed by a short vascular bundle, which is 

 first evident about the time that the number of sporogenous 

 cells is complete, and joins directly with the young vascular 

 bundle of the leaf segment (Fig. 148, C) . The ripe sporangium 

 opens by a transverse slit, as in Ophioglossum. 



The presence of fungous filaments in the roots of the 

 Ophioglossacese has been repeatedly observed, and has been the 

 subject of recent investigations by Atkinson (2), who is inclined 

 to regard them as of the same nature as the mycorhiza found 

 in connection with the roots of many Dicotyledons, especially 

 Cupuliferse. Atkinson asserts that he finds them invariably 

 present in all the forms he has examined ; but Holle ( i ) states 

 that, while they are usually present in Ophioglossum, he has 

 found strong roots entirely free from them, and that in Botry- 

 chium rutafolium they were mainly confined to the diarch roots, 

 and that this is connected with a weakening of the growth of 

 the root through the growth of the fungus, by which the triarch 

 bundle of the normal fully-developed root is replaced by the 

 diarch form of the weaker one. 



Helminthostachys 



The third genus of the Ophioglossaceae, Helminthostachys, 

 with the single species H. Zeylanica, is in some respects inter- 



