and its Mycorhiza. 347 
that cell ; and that this substance is constructed most feebly in the 
sheath, and most vigorously in the mediocortex. 
But the Influence of the nucleus of the host-cell is 
marked In another direction. Near it, in the mediocortex and 
exocortex, the bladders with their rich proteid contents form ; 
that is, there Is abnormal thickening of the hyphae. Miyoshi, 
in the paper already quoted, shows that increasing the concen- 
tration of the nutritive liquid (which also acted chemotropically) 
causes a corresponding Increase In the thickness of the 
hyphae. This at once rouses the obvious suggestion that in 
the mediocortex the protoplasmic bladders form near the 
nucleus of the cell, because it is at that point that the essential 
nutritive solution is most concentrated. Comparing the 
cells of the mediocortex and of the sheath, the effect of the 
position of the nucleus on the thickening of the hypha is 
greatest In the former and least in the latter. And in the medio- 
cortex there is evidence that the substance absorbed from the 
host-cell, leading to the formation of protoplasm, is present in 
largest quantity in the mediocortex, and in smallest quantity 
in the sheath ; for the hypha in the sheath does not branch 
and scarcely thickens, but in the mediocortex great absorption 
and thickening of the hyphae take place. Hence, adopting 
the same line of argument as was used with reference to the 
chemotropically active substance, the conclusion is reached 
that for their thickening and the manufacture of protoplasm the 
hyphae are dependent upon supplies of a nutritive substance 
manufactured by the infected cell , and particularly in the vicinity 
of the nucleus of that cell ; and that this substance is constructed 
most feebly in the sheath , and most vigorously in the mediocortex. 
In this respect, too, the exocortex is transitional between the 
sheath and mediocortex in that a hypha, having entered the cell, 
does not at once pass out, nor does it describe sharp curves, but 
forms broad sweeps and slow curves round the nucleus, and 
In addition to undergoing general thickening (contrast medio- 
cortex) it exhibits slight local dilatations (contrast sheath). 
These last are formed presumably at points which once 
were actually nearer the cell’s nucleus, or physiologically so 
B b 
