KNOWLEDGE OF MONOCOTYLEDONOUS SAPROPHYTES. 159 
Amongst the exocortical cells run a few isolated longitudinal 
rows of raphide-mucilage cells. 
The layers of cortex lying within the exocortex are sharply 
marked off from the latter without any intermediate stages. They 
are larger, and are not radially flattened ; but in transverse section 
are isodiametral. At the base of the root there are about fourteen 
layers of cortical cells lying between the exocortex and the 
endodermis. Where the root has attained its maximum thick- 
ness, there are about double the number of these layers. There 
is, however, a differentiation in these cortical cells. The outer 
cells comprising two-thirds of this part of the cortex are large 
parenchymatous cells elongated in the direction of the axis, and 
with slight collenchymatous thickenings around the small inter- 
cellular spaces. They differ from the cells comprising the inner 
third in their contents, and sometimes fundamentally are distin- 
guished by their form. But these two regions of the cortex are 
not so sharply marked off one from another as they are from 
the exocortex. The great distinction between the two is that 
the outer portion—the mediocortex—usually contains mycelial 
masses, whilst the inner part has no mycelia, and may be 
termed the endocortex. In the roots of this plant the mediocorter 
is further characterized by being extremely rich in starch, even 
where no mycelia are present ; the endocortex, on the other hand, 
has much less starch, sometimes none. f 
In the mediocortex the mycorhiza consists of yellow glistening 
masses not distinguishable into separate hyphe (Pl. IV. fig. 4). 
These masses are connected from cell to cell by their strands, 
which are modified hyphe. Cytoplasm lines the walls and coats 
the mycelial masses, and is packed with countless minute starch- 
grains. A large nucleus is visible in each cell. The mycelia are 
seen to best advantage by staining with Grenacher's hematoxylin, 
washing with increasing strengths of alcohol, clearing with oil of 
cloves, and mounting in Canada balsam. The masses and their 
hyphal strands remain stained, whereas the cytoplasm 1s com- 
pletely decolorized, though the nucleus is deeply coloured. 
Interspersed amongst these cells are longitudinal rows of 
raphide-mucilage cells. With iodine the mucilage stains beauti- 
fully in tints varying from pink to crimson-violet, according to the 
strength of the solution employed. Each mature cell (E LIV. fig. 4) 
shows a group of raphides embedded in a deeply stained central 
