MR. A. J. EWART ON ASSIMILATORY INHIBITION. 429 
this takes place when the amount of carbohydrate (starch and 
sugar) reaches from 17 per cent. to 25 per cent. the dry weight 
of the leaf. As soon as a leaf-cell contains 2 per cent. of sugar 
the conversion of this into starch commences, but when the 
amount of starch has reached its maximum, the leaf-cell still 
continues to assimilate until it contains sugar of from 6-per-cent. 
‘to 8-per-cent. concentration, and is no longer plasmolysable by 
‘a 10-per-cent. solution of glycose. 
In a later paper Saposchnikoff * finds that isolated leaves of 
Vitis vinifera, after 6 to 7 days’ exposure to light, can form no 
more carbohydrates, and then contain of carbohydrates 23 per 
cent. to 29 per cent. of the dry weight of the leaf, there being 
very little difference between the results given by leaves with 
their stalks in distilled water and others with their stalks in a 
nutrient solution. If the leaves are kept in an atmosphere con- 
taining at the commencement 20 per cent of CO,, in 3 days the 
maximal accumulation of carbohydrates is produced, and this is 
from 30 per cent. to 35 per cent. of the dry substance of the 
leaf, this greater amount being probably due to the leaf remain- 
ing more normal in the shorter time of exposure. 
If the accumulation of carbohydrates eventually causes a 
stoppage of assimilation, it must also involve a cessation of all 
evolution of oxygen. Hence the Bacterium method affords a 
ready means of confirming and extending Saposchnikoff’s obser- 
vations, especially as regards the recovery or non-recovery of 
assimilation on the diminution or removal of the accumulated 
carbohydrates. 
Effect of the Accumulation of the Assimilatory products 
(Carbohydrates) upon Assimilation. 
The adult leaves cut with the upper part of the petiole attached 
are kept with their stalks in water exposed to the brightest 
diffuse light, but shielded from too intense and prolonged sun- 
light. 
* * Beitrag zur Kenntniss der Grenzen der Anháufung vom Kohlenhydraten 
in den Bláttern," in Ber. d. D. Bot. Ges. Bd. xi. 1893, p. 391. 
202 
