436 MB. A. J. EWART ON ASSIMILATORY INHIBITION. 
ceases (external action); but, according to Saposchnikoff, im: 
Phanerogams, when sugar accumulates in the cell-sap as a pro- 
duct of assimilatory activity, as soon as the latter contains 8 per 
cent. of glucose further assimilation ceases (internal action). 
The stoppage of assimilation which occurs when the maximal 
accumulation of carbohydrates is reached, is undoubtedly largely 
due to the fact that the sugar can no longer be converted into 
starch and accumulates in the cell-sap till the assimilatory limit 
is reached, but is also partly a direct effect of the accumulation 
of starch in the chlorophyll grain, for, as will be seen later, in 
certain cases, under circumstances in which no large amount of 
sugar can be present, an excessive deposit of starch in the chloro- 
phyll grain is accompanied by a cessation of the power of assimi- 
lation. Dehnecke came to the conclusion, from the well-known 
fact that in many chlorophyll grains a large deposit of starch may 
take place, though the amount of assimilation they can possibly 
have carried on can only have been trifling, that green chlorophylt 
grains, which have as their sole function that of a leucoplastid 
and have no power of assimilating, are of common occurrence in 
green plants, 
Pellionia Daveauana affords very good material for testing the 
truth of Dehnecke’s conclusions. In the stem of this plant the 
parenchyma-cells contain special small amyliferous chlorophyll 
grains. In the young stems and petioles the chlorophyll grains 
in the outer half of the stem contain little or no starch; the 
central cells are larger, and in them each chlorophyll grain forms 
a green plate or flattened cap on the end of a large starch grain. 
The chlorophyll grains are, when without starch, round and about 
3 to 2 the size of those of the leaf mesophyll, and each cell of 
the stem parenchyma contains from six to a dozen. The outer 
cells of the stem contain about 2 to =, the amount of chlo- 
rophyll that the leaf-cells do. Nevertheless, from them on 
exposure to light a weak evolution of oxygen can be detected, 
but none from the inner starch-loaded cells. In the older basal 
parts of the stem all the parenchyma is amyliferous, the starch 
grains being much larger and almost entirely filling up the cavity 
of the cell. Here no power of assimilation can be detected. 
The question is, whether with the removal of the starch the 
power of assimilation returns to these leucoplastic chlorophyll 
grains. To remove the starch, the plants may either be kept in 
the darkness or exposed to light in an atmosphere free of CO, 
In the latter case, after 10 days’ exposure at 20° C. to 25° C., 
