42 Rhodora [Marcu 
may pass the first growing season and the first winter of dormancy 
as rootless, leafless whitish bodies. In this condition I have found 
that they exhibit all the phenomena associated with the presence of 
endotrophic fungi. It is yet to be proved that without the presence 
of the fungus they are able to make use of the soluble organic com- 
pounds that may be found in the surrounding humus. 
The endotrophic fungi of orchid mycorrhiza are made up of closely 
related species. This is clearly demonstrated by an examination of 
pure cultures taken from plants of widely separated orchid genera 
that inhabit different geographical areas. The behavior of the fungus 
within the orchid and the relation of the orchid to the presence of 
the fungus is similar in all the species that I have examined. This 
similarity of behavior and the close structural resemblance that is 
evident among the species of the fungus, indicates a long associ- 
ation between the fungi and orchids. It is pardonable to suppose 
that the present day endotrophic fungi of orchids represent very 
closely what must have been the ancestral form, that is, the form 
which may have had much to do with the evolution of the orchid 
family. This assumption is warranted by the fact that despite the 
vast host of orchid genera and species, there are very few species of 
endotrophic fungi. It is assumed that the fungus has not changed 
much since the alliance with the orchids was formed because it has 
been removed, by its method of life, from those modifying influences 
that effect an organism that is subjected to the ordeal of competi- 
tion. 
The fungus lives in the protocorm, or in the upper cortical tissues 
of roots in adult plants, and is capable of luxuriant development. 
The hyphae do not enter the epidermal cells and are never found in 
the vascular tract. They may pass through the hair-like organs 
already described and are therefore able to carry on the functions of 
the fungus both within and without the body of the protocorm. As 
the fungus passes from one generation of seedlings to another it is 
removed from the necessity for reproduction by spores and perhaps, 
under natural conditions, does not live for any length of time, if at 
all, as an autonomous organism. When in association with orchids 
it is supposed to supply food materials in an available form or to render 
soluble organic compounds assimilable. It surely derives some bene- 
fit for its munificence. In Goodyera pubescens the fungus lives through- 
