KNOWLEDGE OF MONOCOTYLEDONOUS SAPROPHYTES. 157 
Protruding into the cavity of these thick-walled cells are fre- 
quently certain peculiar papille which are attached to the thick 
wall (Pl. IV. fig. 4). They are especially seen on the thick 
tangential walls, pointing radially into the cavity of the thick- 
walled cells or of the subjacent cells, but everywhere are only 
on thick walls. They look like processes of the cell-wall, do 
not swell in sulphuric acid, but in general answer the tests for 
cuticle. Their nature will be discussed later in the paper. 
Within, there typically succeed three peculiar layers of the 
cortex. These are sharply marked off from the cells lying 
more deeply by their shape, size, and contents. As these peculiar 
cortical layers are met with in other saprophytic orchids, I pro- 
pose to allude to them collectively under the name of exocortex 
(PL IV. fig. 4). The cells comprising the three layers of the 
exocortex have thin cellulose walls; they are flattened radially, 
elongated tangentially and in the direction of the root-axis. 
They contain living protoplasm, little or no starch, and many of 
them have mycelia in which the hyphe are distinct from one 
another. With regard to the mycelia, many of the cells of 
the outer two layers have no hyphæ, the latter often passing 
directly radially inwards to the third (innermost) layer, the cells 
of which usually contain mycorhizal hyphe with thick glistening 
walls. The hyphe in the two outer layers have, as a rule, thin 
walls. 
Occasionally a curious distribution of starch may be seen in 
the exocortex. In certain spots hyphæ can be seen pene- 
trating the superficial cells and passing radially inwards through 
the exocortex, scarcely spreading at all tangentially till the third 
layer is reached. In these cells traversed by hyphæ no starch 
is visible. But in the cells which have no mycelia starch is 
found abundantly. These latter cells do not absorb from the 
exterior, as a thick-walled layer is invariably external to them, 
and no hyphe penetrate the thick walls to permit inward pas- 
sages of liquids. Thus these starch-containing cells merely 
receive food supplied by the cells containing hyphe. 
In parts of the root some of the eells immediately beneath the 
external layer have thick cuticularized walls, and they form 
patches of thick-walled tissue lying in the exocortical region. In 
such cells peg-like papillæ, identical with those described, are 
frequently found protruding from the walls. In favourable 
sections it may be seen that the pegs protrude into the cells only 
