ON THE MYCORHIZAS OF FOREST TREES 
55 
Form I. — This form is found on Carya ovata and is, when fresh, 
bright yellow in color. A superficial examination with the binocular 
microscope, or a good pocket lens, reveals a network of mycelium 
over the surface and numerous short hyphae projecting out from it. 
A cross section of this mycorhiza (fig. 2), shows the following parts, 
beginning at the center: (i) The central cylinder; (2) about three 
circular rows of ordinary cortical cells; (3) a row of radially elongated 
cells. This row, however, does not extend clear around the section, 
but, on one side of the section, its cells are cut up into a number of 
irregularly shaped cells. The cells of this row are entirely separated 
from each other by fungus tissue which surrounds each cell on all 
sides. (4) Finally there is a layer of fungous filaments surrounding the 
section. From the outer part of this layer, which forms a mantle 
over the entire rootlet, tip and all, there are given off numerous fila- 
ments which project out into the surrounding soil. From the inner 
part of this fungus layer there are given off the filaments which sur- 
round the radially elongated cells as described above. 
Form 2. — A second form, found also on Carya ovata, is brown in 
color when fresh. In microscopic section the same general parts are 
distinguished as in the form described above. The structural differ- 
ence is concerned principally with the fungus mantle (fig. 3.) This 
instead of being made up of easily distinguishable filaments, consists 
of a pseudoparenchymatous tissue, such as is found in many lichens. 
The outer surface of this mantle is smooth ; that is, there are no hyphae, 
or very few, projecting out into the soil. From the inner part of the 
mantle, hyphae extend inward between the cells of the root as in the 
former case. In the latter case, however, they often extend in farther 
than the single external layer of cells, and they are all divided up into 
short cells, so that the pseudoparenchymatous character is observed 
here as well as in the mantle. 
Form J. — Still another form, also found on Carya ovata, is white 
when fresh. The fungus mantle, in this case, is distinctly filamentous, 
but the outer surface is smooth as in the last described form (fig. 4). 
The root istelf and the fungus parts projecting into the root are practic- 
ally of the same structure as in the first described form. 
Form 4. — A fourth form found on Quercus alba is white when fresh. 
The clusters often lie more or less in one plane, as if they had been 
pressed, and they appear more or less wooly. The filamentous mantle, 
in this case, is very loosely constructed, and is easily torn and broken 
up while the microtome sections are being prepared. 
