PLANT PHYSIOLOGY 245 



glycogen in animals. The glucose and maltose formed from 

 the starch which in turn was formed from photosynthesized 

 glucose, is carried by the sap throughout the plant, where it 

 undergoes further metabolism, as previously stated. 



Part of this glucose is carried to other organs of the plant, 

 viz. the seeds, tubers, roots, etc., which are reserve organs for 

 the storage of starch food. In these reserve organs the sugars 

 are again converted into starch and here the starch acts as re- 

 serve food for renewed growth in the germ, buds, twigs, etc. 



Germination. — Roughly speaking, the seed of a plant con- 

 sists of a germ which is surrounded by a reserve supply of food 

 on which the new plant lives for the first period of its life. 

 This reserve food consists of all three of the essential organic 

 constituents, carbohydrates, fats and proteins, and also in- 

 organic constituents or salts. The carbohydrate food in the 

 seed consists usually of starch, though this may be replaced by 

 sugars, reserve cellulose or inuHn. When the germ begins to 

 grow these food materials are gradually assimilated. 



In order to be used as food by the developing germ the starch 

 is again hydrolyzed into maltose and glucose. This hydrolysis 

 is brought about by the same enzymes as are active in the 

 leaves, viz. diastase and maltase. This diastase of the seed, 

 while considered to be the same enzyme as is present in the 

 leaves, acts somewhat differently physically ; and to distinguish 

 between the two the one in the seed is called diastase of secretion 

 and the one in the leaves diastase of translocation. 



The isolation of diastase and maltase from germinating seeds 

 and their hydrolytic action upon the starch of the seed, yield- 

 ing glucose, has been fully established experimentally. In fact 

 both the enzyme maltase and the sugar maltose, or malt sugar, 

 upon which it acts, derive their names from the fact that they 

 are present in, and can be easily isolated from, malt, which is 

 germinated grain, usually barley. 



Thus we see that one of the results of carbohydrate synthesis 

 in green plants is to produce food material either for the plant 

 itself or for the germ of its offspring. 



