KNOWLEDGE OF MONOCOTYLEDONOUS SAPROPHYTES. 209 
largely stored in the adjoining cells. But this fact might be 
interpreted in many different ways. 
The next point in the histology of the absorbing-organs is the 
large size of the cortex and the smallness of the central cylinder 
(excepting Epipogum nutans). These organs have usually to 
act as food-reservoirs till the inflorescence-axis shoots up and the 
stock of food demanded. In the plants investigated there is a 
tendency for the outer layers of the cortex to entertain, throughout 
life, active mycorhizal mycelia and to form a distinct exocortez 
(roots of Galeola, Aphyllorchis, Lecanorchis, Neottia (according to 
Drude); rhizomes of Epipogum aphyllum and Corallorhiza innata). 
This layer is represented in Epipogum nutans by the adpressed 
scales coating the rhizome. In the young stages the active mycelia 
descend into the deeper layers of the cortex, and may even reach 
the endodermis. Usually these mycorhizal hyphe which lie more 
deeply are soon converted into inert highly refractive masses. 
The cortical tissue within the exocortex is characterized by being 
a receptacle for the storage of food (starch); and it may be dif- 
ferentiated into a mediocortex and an endocortex, the latter of 
which is never penetrated by the mycorhizal fungus (e. g., roots 
of Galeola, rhizomes of Epipogum aphyllum, Corallorhiza innata). 
Only in one case was there any indication of the solution of the 
dead mycelial masses, namely, in Lecanorchis. The structure of 
the central cylinder of the roots is normal, excepting that there 
is a tendency for the conducting constituents of the xylem to 
dwindle. In absorbing-rhizomes the central cylinder, even in 
Corysanthes, tends to become root-like in appearance, and the 
xylem is very reduced. We can possibly associate the reduction 
of the vessels with the fact that absorption takes place at all 
regions of the absorbing structure (not merely near the apex), 
and can compare this with the reduction in such epiphytes 
as Aeranthus and Tillandsia usneoides, or with submerged aquatic 
plants. . 
In Epipogum nutans, on the other hand, the cortex is small 
and devoid of mycorhizal hyphe. The stele is large and the 
conducting elements of the xylem greatly developed. 
Structure of rhizomes which do not absorb solutions.—As there 
appears to be no mechanism by which the roots rid themselves of 
the excess of water absorbed, and as the nutrient substances 
must be conveyed sooner or later into, or through, the rhizome, 
it seems a priori probable that most of water absorbed by all 
