Notes . 
281 
There are, however, serious objections to this simple explanation. 
One of them is that the observed increase in diastase is out of all 
proportion to the starch actually dissolved. We should in fact expect 
a very much smaller increase in the diastase than is actually observed. 
Moreover this view necessarily postulates a constant formation and 
re-dissolution of starch as going on simultaneously in the same cell , a 
condition of things very unlikely to occur, for it is very difficult to 
imagine that solid starch can be deposited from some such pre- 
existent form as soluble-starch at a time when the cell contains far 
more than a sufficiency of diastase to hydrolyze that starch completely. 
Our own observations on the leaf of Hydrocharis are altogether 
opposed to the view that formation and dissolution of starch can take 
place simultaneously in one and the same cell. 
A more probable explanation of the increase of leaf-diastase in 
darkness was suggested by some observations which we have described 
in an earlier paper on the Germination of the Grasses 1 . We there 
showed that the epithelium of the scutellum must be regarded as a 
specialized tissue for the secretion of diastase by the embryo of the 
Grasses, and we also showed that this power of diastase-secretion is 
inhibited in a remarkable manner as long as the embryo is artificially 
supplied with solutions of certain sugars, and is therefore not obliged 
to obtain its nourishment from the starchy reserve-materials of the 
endosperm. The secretory function of the epithelium is in fact only 
exercised when the embryo is in danger of starvation. 
We find that a somewhat similar explanation is applicable to the 
increased production of diastase in leaves when these are placed in 
the dark. 
As long as the conditions are favourable for assimilation, the leaf- 
cells are necessarily supplied with an abundance of newly assimilated 
materials in the form of sugars, more in fact than can be easily made 
use of or translocated. The excess of nutritive material is in part 
deposited as starch. 
At this period there is little or rlo elaboration of diastase by the 
cell-protoplasm, probably none at all in those cells in which starch- 
deposition is actually going on. 
When the light fails and assimilation consequently falls off, the 
living cells speedily use up or translocate the excess of assimilated 
1 Journ. Chem. Soc., vol. lvii. p. 458, 1890. 
