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 sugar continues to be withdrawn from the 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 oxidation 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 



