164 THE AMERICAN NATURALIST [Vol.XLII 



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 digestive cells. 

 This seems plausible from the fact that in green pro- 

 thallia, where presumably the plant is entirely able to 

 supply its own carbon compounds through photosynthesis, 

 these digestive cells appear to be wanting; or at any rate 

 they were not observed in the several forms that T have 

 studied. The experiments of Ternetz already referred 

 to showing that certain fungi, including certain endo- 

 phytic mycorhiza*, have the ability to assimilate free 

 nitrogen, confirms the assumption of earlier authors that 

 the fungus is useful to the host in supplying to it nitro- 

 gen compounds; but while this is probably a very impor- 

 tant part of its functions, it seems to me that it is not 

 perhaps the only one, and that the necessary carbon is 

 also supplied directly or indirectly through the agency 

 of the fungus. 



As Magnus has very graphically shown, the relation 

 of the two symbionts is mutually antagonistic each one 

 acting as a parasite on the other, but nevertheless the 

 presence of the fungus is essential to the higher organ- 

 ism so long as the latter is destitute of chlorophyl; and 

 the explanation of the wide-spread 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 feed upon the parasite, the photo- 

 synthetic functions were more and more subordinated 



suited. The numerous semi-saprophytes like most of 

 the green Ericacea> and many green Orehidacew are good 

 examples of transition stages, while the characteristic 

 leafless humus saprophytes, such as the Monotropeae and 

 the chlorophylless Orchidaceae, represent the fully de- 

 veloped phase of this peculiar form of symbiosis. 



