244 ORGANIC AGRICULTURAL CHEMISTRY 



the building up of body substance or for storage as reserve food. 

 The sugars are carried by the sap to all of the plant cells, and 

 in the cells they undergo metabolic changes whereby they yield 

 energy, form body substance or are converted into reserve food. 



Starch. — In two localities, in particular, do we find the sugar 

 glucose thus metabolized into the polysaccharose starch. 



Reserve Food. — In both of these places the starch is reserve 

 food. In the leaves of plants starch is always present. In 

 fact it is so universally present here and follows so closely the 

 photosynthetic activity that it was long believed to be the 

 direct product of photosynthesis. It is probable, however, 

 that glucose is first formed and the starch then produced by 

 enzymatic action, involving loss of water and condensation or 

 union of the unit glucose molecules into larger starch molecules. 

 Though starch is constantly being thus formed in the leaves, it 

 does not accumulate but is continually reconverted into maltose 

 or glucose and carried away by the plant sap. This is clearly 

 shown by the disappearance of the starch in leaves during 

 darkness, when photosynthesis is not going on. In the morn- 

 ing, following the darkness of night, practically all starch has 

 left the leaves. This conversion and translocation of starch in 

 the form of glucose is being carried on during the day as well 

 as during the night, but as new starch is being continually 

 formed at the same time, the translocation does not show as 

 well as at night. The conversion of glucose, the product of 

 photosynthesis, into starch which is immediately reconverted 

 into glucose for translocation is quite closely analogous to the 

 process in animals whereby absorbed carbohydrate food in the 

 form of glucose, fructose or galactose is converted into glycogen 

 in the liver and the glycogen then continually reconverted into 

 glucose and sent out in the blood to all parts of the animal. 



Diastase and Maltase. — The conversion of starch in the 

 leaves into glucose is brought about by enzymes known as 

 diastase and maltase. These two enzymes convert starch first 

 into maltose sugar and then into glucose. The starch in the 

 leaves thus acts as a temporary reserve material very like the 



