32 THE OPHIOGLOSSALES 



into the receptive prominence. A similar synapsis was noted in several cases. In 

 most instances where free spermatozoids were present in the venter of the arche- 

 gonium the egg nucleus presented a curious appearance (plate 2, figs. 47, 48). A 

 single large nucleolus was present, but scattered through the nucleus there were 

 sometimes a dozen or more of intensely staining round bodies, which at first sight 

 looked like nucleoli, but on more careful examination were seen to diflFer from 

 the large nucleolus in that they appeared less homogeneous and generally showed a 

 central vacuole-like structure. These granules stain very much like the body of 

 the spermatozoid, and it was thought that possibly they might be derived from a 

 fragmentation of the body of the spermatozoid that had entered the nucleus, but 

 this could not be satisfactorily demonstrated and the nature of this phenomenon 

 must remain for the present uncertain. 



Fertilization in Helminthostachys has not been observed. 



SIGNIFICANCE OF THE ENDOPHYTE. 



That the presence of the endophyte is essential to the existence of the sapro- 

 phytic gametophyte of the Ophioglossaceae is indicated by the failure of the germi- 

 nating spores to develop unless they become associated with the fungus. Moreover, 

 the universal occurrence of a similar endophyte in all humus saprophytes among 

 the seed plants indicates that in all of these chlorophyll-less plants the presence of the 

 fungus is necessary for the existence of the host. Although it has not been directly 

 proved, it is generally assumed that one role of the endophyte is the elaboration of 

 some of the carbonaceous constituents of the humus. The infrequent communica- 

 tion between the external hyphae and the internal mycelium makes it unlikely that 

 the nutritive products are directly absorbed by the fungus, and it seems much more 

 probable that the rhizoids of the gametophyte are the direct agents of absorption. 

 How the humus constituents are changed by the action of the fungus so that they 

 are available for the cells of the host is not clear, and it is by no means impossible 

 that some at least of the necessary carbon may be derived from the fungus itself, 

 in the digestive process to which it is subjected in the cells of the host. This seems 

 plausible from the fact that in the green prothallia of certain ferns, where presumably 

 the gametophyte is entirely able to supply its own carbon compounds through 

 photosynthesis, these digestive cells appear to be wanting; at any rate they were not 

 observed in a number of forms that I have studied. 



The experiments of Ternetz (Charlotte Ternetz 1), show that certain fungi, 

 including endophytic mycorrhizae, are able to assimilate free nitrogen and confirm 

 the assumption of earlier observers that the fungus is useful to the host in supplying 

 it with nitrogen compounds; but, while this is probably a very important part of 

 its functions, it seems to me that it is not perhaps the only one, and that the carbon 

 also is supplied, directly or indirectly, through the agency of the fungus. 



In an extended study of the endophytic mycorrhiza of the saprophytic orchid, 

 Neottia, W. Magnus (W. Magnus 1) has shown that two types of mycelium ex- 

 hibited by the endophyte are of very different nature. The slender, cylindrical 

 hyphae constitute the active portion of the fungus, which behaves like a parasite 

 toward the cells which it invades, destroying the starch and probably other constitu- 

 ents of the cells, but not attacking the nucleus. The swollen vesicular mycelium, 

 however, is a degenerating structure and is itself destroyed by the cells of the host, 

 which actually digest these fungus mycelia in much the same way that the cells of 

 the leaf of Z)roj-^ra digest their prey. Magnus has very graphically shown that the 

 relation of the two symbionts is mutually antagonistic, each one acting as a parasite 

 on the other; nevertheless the presence of the fungus is essential to the higher 



