156 MR. P. GROOM—CONTRIBUTIONS TO THE 
vascular bundles are well defined, that mucilage and raphides are 
abundant, and that in the placente there is a large development 
of mucilage-producing tissue. 
The subterranean part of the plant consists of a large mass-of 
succulent roots attached to a small irregular rhizome (fig. 1) 
The whole mass measures 5 inches in length, the longest root 
being 4 inches long. 
Roots. 
The roots are all succulent and unbranched, and they vary in 
length. Each root at its point of attachment is about a quarter 
of an inch in thickness; travelling towards its apex, it rapidly 
increases in thickness till its diameter is about half an inch; 
the root maintains this thickness till it ends bluntly at its 
apex. 
Histology of the Root. 
In their minute structure the roots vary considerably in their 
different parts. 
Describing first the mature structure of the root :— 
The first characteristic of the root is that it is not covered by 
any definite layer of cells. In some regions a piliferous layer is 
represented by a larger or smaller patch of relatively not thin- 
walled cells united without intercellular spaces. They contain 
dense coiled masses of hyphw (mycorhizal), cytoplasm, and well- 
defined nuclei. A few of these cells grow out into short, broad, 
thick-walled cuticularized root-hairs. The root-hairs tend to lie 
flat on the surface of the root in place of protruding freely. 
Hyphe occur in the root-hairs. But over the larger part 
of the root there is no trace of this piliferous layer, the super- 
ficial layer being irregular, and formed of cells with very thick, 
pitted, suberized walls (Pl. IV. fig. 4). These cells are elongated 
in the direction of the root-axis. Thus, the surface is uneven, 
and in many places there is clearly no regular layer of cells; 
even mucilage-sacs may reach the surface. But whatever layer of 
the cortex forms the superficial cells, the cells assume the same 
character as regards the thickness and suberization of their walls 
(Pl. IV. fig. 4), always excepting the primary piliferous layer. 
Mycorhizal hyphe may be seen running through these cells from 
the outside to the cells lying within. Even when the piliferous 
layer persists, the subjacent layer has thick suberized walls; 
but there is no definite regular exodermis. 
