56 



PLANT PHYSIOLOGY 



To become acquainted with the course of hydrolysis in germi- 

 nating seeds and living cells in general, it is necessary first to 

 examine the case of hydrolysis of reserve carbohydrates, viz., 

 of starch. Microscopic observations have shown that from the 

 first days of germination, starch undergoes an intensive chemical 

 transformation. On the surface of the grains of starch, first 

 appear small depressions, which gradually deepen into the grain. 

 By the union of these depressions and the formation of cavities, 

 the starch grain finally becomes so tunneled that it falls apart 

 into minute granules, which in the end are completely dissolved 

 (Fig. 14). In place of starch, there now appear sugars, viz., 



Fig. 14.- 



••;-.;;.,'&r.;as;*;.-v 



-Successive stages in the direction of a starch grain by diastase (Srfter 



Benecke-Jost). 



maltose and glucose. It is easy to detect this accumulation of 

 sugar by special reagents, such as Fehling's solution, or simply 

 by tasting. The ungerminated grain of barley has a mealy 

 taste, while the germinating one is sweet. Germinated barley 

 after drying is called ''malt" and is used extensively in brewing 

 and other industries. 



The germinating seed does not have at its disposal those 

 agents, such as strong acids and high temperatures, by which 

 the hydrolysis of polysaccharides, is brought about in a labora- 

 tory. It does, however, have substances capable of bringing 

 about this hydrolytic cleavage even at ordinary temperature. 

 These substances are known as ''enzymes." One of the first 

 substances of this sort to be discovered in plants was the enzyme 

 that hastens the decomposition of starch, known as "diastase" 

 or ''amylase." 



