58 
W. B. McDOUGALL 
and under the same tree, a considerable number of sporophores of 
Cortinarius sp. were found, and their connection with mycorhizas 
was demonstrated. 
Finally, on the i6th of September, 1912, a fourth mycorhiza pro- 
ducing fungus was .found, this time a puff-ball, Scleroderma vulgare 
Fr. This fungus causes the white mycorhizas which were described 
above as Form 4, and which occur on Quercus alba. A large number 
of the fruiting bodies were found and the pure white rhizomorphs made 
it comparatively easy to trace the hyphae from the mushroom to 
the mycorhiza. 
3. Number of Species of Fungi which may Cause Mycorhizas on the 
Same Tree 
The mycorhizas of Betula, caused by Cortinarius and Boletus, 
are easily distinguished from each other, since those caused by Cor- 
tinarius are brown, while those caused by Boletus are white. They 
differ also in the structure of the fungous mantle. In the Boletus- 
Betula mycorhizas the mantle is very compact and smooth on the 
outside, as in fig. 4, while in the Cortinarius-Betula mycorhizas the 
mantle is of a rather loose filamentous structure, and has hyphae 
projecting out into the soil (fig. 5). 
If, now, on other trees, mycorhizas which differ greatly in color and 
structure are found, it may safely be concluded that they are caused 
by different species of fungi. Such a case was observed on Carya 
ovata. The first three mycorhizas described in this paper were all 
found on the same individual Carya, and differed from each other both 
in color and structure. Moreover, all three forms do not occur on 
this tree every year. In 191 1 all three forms were found, the yellow 
form being much the most abundant; but in 191 2 the yellow form 
was not present at all, while the white form was very abundant. The 
brown form was found both years in about the same numbers. 
On Quercus alba, again, four forms of mycorhizas were found on the 
same tree, one of which differs from the other three in color, and all 
of which differ from each other in structure. Three of these are brown 
in color and correspond in structure to the first three forms described 
above. The fourth is the one which was shown to be caused by 
Scleroderma vulgare, and, since the mycelium of this fungus is pure 
white, it is not possible that it could be the cause of any of the brown 
forms. There is no doubt, then, that these four Quercus mycorhizas 
are caused by four different species of fungi. 
