349 
and its My cor hi za. 
phores seem always to aggregate round the nucleus, and 
starch therefore frequently appears first in this circumnuclear 
region. So there is evidence that in plant-cells the manu- 
facture of solid carbohydrates is influenced by the nucleus. 
But Demoor, by the use of chemical substances (chloroform) 
and by intense cold, succeeded in producing in Spirogyra 
a peculiar condition of the cell, in which the nucleus divided, 
but the cell-wall was not formed between the two nuclei. 
However this observation does not prove that the nucleus 
was the only active part of the protoplasm, nor does it 
necessarily imply, on the other hand, that we must ascribe to 
cytoplasmic activity any initiatory share in the formation of 
the cell-wall. Haberlandt showed as a matter of fact that 
the nucleus of plant-cells often wanders towards that part of 
the cell-wall at which irregular thickening is taking place ; 
and this observation seems of more value than those in which 
the protoplasm was brought into a pathological condition by 
excision of the nucleus or use of abnormal stimuli. Animal 
physiologists have also conducted observations which have 
led them to conclude that the nucleus influences, or even 
controls, the metabolism of a cell in some directions (processes 
of secretion of calcium carbonate, mucilage, and animal 
cuticle 1 ). 
To sum up : the distribution, form, and mode of development 
of the mycorhizal hyphae of Thismia are dependent on their 
constant chemotropic character , on the location of the cell infected , 
and on the metabolic processes taking place in that cell, particu- 
larly near its nucleus . 
And doubtless this generalization holds, at any rate for 
orchids and Marattiaceae. For in the mediocortex the 
mycelia only differs from those in Thismia in that numerous 
slender hyphae grow out from the primary bladder, and in 
the subsequent changes said to occur in these hyphae. 
1 Max Verworn, Allgemeine Physiologic, contains references to all the papers 
quoted. M. Verworn puts forward the view that the nucleus influences the 
metabolism of a cell in a manner analogous to a chloroplast. See his article Die 
Physiologische Bedeutung des Zellkerns, Pfliigers Archiv, Bd. li. pp. 1-118. 
B b 2 
