1893.] Symbiosis and Mutualism. ; 515 
ium does not necessarily imply the presence of the perfect 
fungus fructification, as mycelia may, and often do, go on 
growing in a sterile condition for years. 
Frank did not stop here. He found symbiotic fungi on the 
roots of many other trees, and others after him found mycelia 
on the roots of various plants to which he attributes the same 
relations of mutualism. His final statement is that this phe- 
nomenon belongs “ to all trees under certain conditions ; ” that 
“the Mycorhiza is formed only in a soil which contains 
humous constituents or undecomposed vegetable remains; ” 
that “the development of Mycorhiza increases or diminishes 
with the poverty or richness in these constituents ; ” and that 
“the fungus of the Mycorhiza conveys to the tree, not only the 
necessary water and the mineral nutritive substances of the 
soil, but also organic matters taken direct from the humous 
and decomposing vegetable remains.” Finally, he claims that 
only through the fungus can the tree employ such organic 
matter directly. 
If the fungus develops only in soil containing undecomposed 
vegetable remains, we might ask why it takes the trouble to 
attach itself symbiotically to the root and give the tree the 
benefit of its saprophytism; especially, as Frank says that 
the protoplasm of the cells and the fungus live together “ with- 
out the former being parasitically affected or its vital phe- 
nomena disturbed.” This reminds one of the exhausted gon- 
idial cells which are still uninjured, and is not the only one 
of Frank’s statements calculated to try our patience. and cred- 
ulity. 
In 1886, Warlich (Botanische Zeitung, 1886, p. 481, et seq.) 
investigated certain fungi on the roots of orchids. He 
examined several hundred species, all of which he found 
affected on both aerial and subterranean roots with the 
mycelia of what he showed to be a species of Nectria. The 
-hyphe of this fungus affect spots here and there, forming 
knots or coils in certain cells and causing them to enlarge, 
but, as a rule, only partly filling the cell and not destroying 
the protoplasm. Frank, of course, took this up, and he claims 
that the protoplasm of the cell is not affected or disturbed by 
