54 
W. B. McDOUGALL 
tance from the tree, dig until mycorhizas are found, and then, after 
collecting the specimens, carefully trace back the root until it is 
determined to what tree it belongs. 
As equipment for the work of collecting I usually carry a spade, 
a garden trowel, and a small hunter's axe, besides a knapsack for hold- 
ing a notebook and bottles for specimens. The specimens, when 
collected, were either put at once into i per cent chrom-acetic acid, 
or carried to the laboratory in water, and then killed in the acid. 
During the winter, when the soil was frozen, solid pieces of soil were 
chopped out with the axe, and those pieces that were thought likely 
to contain small roots, and, therefore, possibly mycorhizas, were taken 
into the laboratory and thawed out, when the mycorhizas, if present, 
could be picked out. Specimens collected in this way were always 
taken from places where the roots had been identified and their 
positions marked during autumn. In preparing specimens for study 
they were embedded in paraffin, sectioned by the microtome, and 
stained with gentian violet and fuchsin. 
3. The Glass Plate Method of Study 
Besides the method of study just outlined, the mycorhizas were 
studied as they grew in their natural habitat by the following method : 
the humus and leafmold were scraped away from a small area until 
some mycorhizal roots were uncovered. A round glass plate about 
eight inches in diameter was then placed over these roots, pressed down 
firmly, and covered with soil. Care must be taken that no air-spaces 
are left beneath the glass, and the glass must be well covered; other- 
wise the roots will wither and die.. It is usually necessary to remove 
the glass when an observation is to be made. 
III. OBSERVATIONS AND EXPERIMENTS 
A. EcTOTROPHic Mycorhizas 
I. Descriptive 
Ectotrophic mycrohizas are easily recognized by the characteristic 
clusters of numerous, short, stubby branches which have been de- 
scribed as coral branching rootlets (fig. i). When alive, they always 
have a bright, fresh appearance, even when collected in midwinter. 
They vary in color from white to bright yellow, brick red, or dark 
brown. They also vary greatly in the character of the external 
surface and internal structure. The different forms will therefore 
be described separately, as follows: 
