THE GAMETOPHYTE 33 



organism, so long as the latter is destitute of chlorophyll. The explanation of the 

 widespread saprophytism exhibited by so many of the higher plants may be sought 

 in this attempt to defend themselves against what was probably at first a strictly 

 parasitic organism. Having acquired the power to attack and to feed upon the 

 parasite, the photosynthetic functions were more and more subordinated, until a 

 state of true parasitism (or saprophytism) resulted. The numerous semi-saprophytes 

 like most of the green Ericales and many of the green Orchidaceae, are good examples 

 of transition stages, while the characteristic leafless humus saprophytes, such as 

 Monotropa and Corallorhiza, represent the fully developed phase of this peculiar 

 form of symbiosis. We might say that such green prothallia as those of the Marat- 

 tiaceae and Gleichenia, which contain an endophytic fungus, bear somewhat the 

 same relation to the subterranean prothallia of the Ophioglossaceae that the green 

 Ericales do to Monotropa. 



The occurrence of a similar endophyte has also been noted in a number of 

 liverworts. Cavers (Cavers 1) has studied this association with some care in the 

 common liverwort, Fegatella, as well as in some other Hepaticae. He found in 

 Fegatella that the endophyte is beneficial to the growth of the host, which was more 

 vigorous when the fungus was present. He assumed that this was due to the assist- 

 ance given by the fungus in the assimilation of organic matter from humus or other 

 organic substrata. (See also Humphrey 1). 



This occurrence of an endophyte in the Hepaticae makes its occurrence in the 

 green prothallia of ferns readily comprehensible. Whether in the latter it is an 

 advantage to the host to have the endophyte present remains to be seen, but it 

 is highly probable that such is the case. Once having acquired the habit of 

 associating itself with the fungus, the gradual evolution of the purely saprophytic 

 subterranean gametophyte of the Ophioglossaceae from green forms similar to those 

 of the Marattiaceae is readily comprehensible. 



