MR. A. J. EWART ON ASSIMILATORY INHIBITION. 435 
of assimilation. The primordial utricle in all cases determines at 
what rate and in what quantity any given substance will pass 
through to the cell-sap. Immersion in a weak sugar solution 
helps to produce the maximal accumulation of carbohydrates 
more rapidly only because it affords another source from which 
carbohydrate material is drawn, and not because of any physical 
diffusion through the primordial utricle and accumulation in the 
cell-sap. 
Immersion in very strong sugar solution causes so marked a 
withdrawal of water as to affect the power of assimilation, and 
finally the vitality of the cell. The plants are placed in solutions 
-of gradually increasing strength until the desired percentage is 
reached, when, after a few hours’ immersion, preparations are 
examined in a 20-per-cent. solution of cane-sugar with Bacteria. 
After being for half an hour in 20-per-cent. and the same time 
in 10-per-cent., the plants are placed in water. 
Elodea After 9-4 hours in 35 p. c. or 6-8 hours in 30 p. c. of cane- 
canadensis. sugar shows, when examined in 20 p. c., no power of 
assimilation, though most cells remain living. In 
10 p. c. a weak evolution of O is shown in most cases, 
which after 1-2 hours in water becomes normal. 
Catharinea | After 12 hours in 35 p. c. or 24 hours in 30 p. c. no 
undulata ; evolution of oxygen is shown under optimal illumi- 
Dicranum nation. Recovery as in Elodea. 
Scoparium. 
Bryum After 1 day in 35 p. c., show in 20 p. e. no evolution of 
cespititium;| O, but assimilation returns on accustoming to water, 
Grimmia and becomes normal in a few hours. After 1 day in 
conferta ; 30 p. c., show in 20 p. e. weak evolution of O in many 
Orthotrichum cases, but in most cases none. After 2 days in 30 p. c. 
affine. some leaf-cells die; rest show no evolution of O. On 
accustoming to water a weak evolution of O is shown, 
which in 1 day is fairly active in all living cells. 
In all cases it is impossible to produce a complete temporary 
stoppage of the power of assimilation without kiling a few 
leaves or leaf-cells, though most remain living and recover. The 
different times necessary for the stoppage of assimilation to 
take place are probably due to differences in the permeability of 
the cell-wall and in the force with which the cell retains water. 
Thus Elodea is very readily plasmolysed, but Catharinea and 
Dicranum much less readily, aud Bryum and Grimmia least 
readily. When the concentration of the cell-sap reaches a per- 
centage equivalent to 35 per cent. of sugar, assimilation soon 
