28 MacDougal. — Symbiotic Saprophytism. 
The radial walls are marked with reticulate thickenings which 
are in general at right angles to the root, and the inner wall 
bears similar thickenings. The lateral and inner walls are 
plainly but sparingly perforate, and the outer wall, especially 
in old cells, appears to be pierced by minute openings. The 
layer is destitute of protoplasm, and the outer wall is seen to 
be coated with humus particles adhering directly to the wall. 
A few of the cells of this outer layer are prolonged outwardly 
into root-hairs which are traversed by fungal hyphae. The 
hyphae are to be found in some of the cup-shaped cells also. 
In many instances, the development of the cell toward the 
root-hairs proceeds only so far as to produce a capitate 
extension outside the bounding line of the organ, very rich 
in hyperchromatic protoplasm. The lateral and inner walls 
of the basal portions of the root-hairs are pitted and furnished 
with short cellulose ridges. 
The second layer consists of irregular thin-walled cells rich 
in protoplasm. The cells underneath the root-hairs are 
enlarged, and the protoplasm is hyperchromatic. The fungal 
hyphae make a few convolutions in these elements as they 
pass to the cortex. The inner epidermoidal layer is com- 
posed of smaller elements often with folded walls, and rich in 
protoplasm. 
The cortex consists of ten to twelve layers of cells loosely 
arranged in radii. A small number contain starch. The 
Fungus is distributed in irregular sections of the outer and 
medio-cortex, vesicles being formed in the neighbourhood of 
the nuclei, connected by two or three filaments only with the 
vesicles in adjoining cells. The cortical cells in the region 
internal to portions inhabited by the Fungus show an in- 
creased radial diameter. 
The vesicles are more or less closely applied to the nuclei, 
which do not differ greatly from the normal in form, size, or 
staining properties. This, and the fact that the chlorophyll- 
surfaces are comparatively limited, leads to the conclusion 
that the fungal symbiont must participate' to a marked degree 
in the acquisition of food-substances. 
