THE GREEN LEAF 69 
If a leaf which has been active enough 
to have accumulated starch in its tissues be 
examined after a sufficient interval during 
which photosynthesis has been in abeyance 
(owing to the absence of light, for example), 
the amount of starch will be found to be 
lessened, and it may have all disappeared. 
The reason of this lies in an extension of 
the process already sketched in outline. The 
sugar continues to be withdrawn from the 
leaf cell even after all further synthesis has 
ceased. But as the concentration of the 
sugar sinks, a ferment action makes itself 
felt within the cell. The starch is gradually 
attacked by a ferment or enzyme known 
as diastase, and it is thus converted into 
a soluble sugar called maltose; the maltose 
then continues to pass away from the cell, or 
at least so much of it as is not immediately 
required by the cell protoplasm itself. The 
process of migration continues till all the 
starch has been fermented and _ rendered 
soluble. 
The change from starch to sugar is a very 
simple one, merely involving a dislocation of 
the larger molecular aggregate together with 
the incorporation of a molecule of water. It 
is of a totally different order of change to that 
which is involved in the oaidation of the 
carbohydrate. For oxidation involves a con- 
siderable change in the state of energy, as 
well as of chemical constitution. 
The leaf starch, thus fermented into soluble 
