12 MacDoiigal. — Symbiotic Saprophytism . 
cells with uniform walls which show oval perforations in the 
older stems. In places the large thin-walled cells of the 
cortex touch the epidermal cells directly. Many stomata 
are to be found opening into distinct air-chambers in the 
cortex. Both arrangements are apparently devices for the 
extrusion of superfluous water, though no direct experimental 
evidence of the fact was obtained. 
The outer layers of the cortex exhibit many mucilaginous 
raphide-cells. In the median regions are many mycorhizal 
clumps of anastomosed filaments similar to those found in 
the root. No uniform distribution is to be made out, how- 
ever, and in any given cross-section these formations may 
be confined entirely to one quadrant. Since the offshoot 
usually is not furnished with trichomes except at the base 
as noted below, there is no external development of the 
hyphae. The sheath consists of an ill-defined layer of pris- 
matic elements with oblique ends, and walls evenly and 
sparingly thickened. In mature offshoots a double ring of 
bundles, with the conjunctive tissue sclerotized, is to be seen. 
The bundles consist of one or two spiral vessels, two or three 
scalariform ducts, and a number of sieve-tubes and companion- 
cells. The space separating the bundles is made up of 
libriform elements with numerous oblique perforations. It 
is to be seen that the offshoot is amply equipped for con- 
duction, and that the cortex affords a ready means of exit 
for superfluous water. 
A clump of trichomes is to be found on the offshoot near 
its base, and in the longitudinal section the fungal cysts are 
seen to occupy a mass of cells increasing in volume from the 
base of the clump of trichomes, and spreading out toward 
the apex of the root, until some appear on the upper side 
of the stele. The fungal hyphae are not to be found on 
the base of the offshoot or in the corm ; and since the off- 
shoot offers no other means of access, it is plain that the 
fungal hyphae from the root-hairs of the parent plant pass 
through the soil, a distance of a few millimeters, and enter 
the offshoot by the hairs near the base. The presence of the 
