3 o THE WHEAT PLANT 



In addition to its absorptive function, the epithelium secretes diastase 

 which is responsible for the conversion of the reserve starch grains into 

 the soluble and diffusible maltose. The aleuron cells also secrete 

 diastase, but to a smaller extent, and according to Griiss, Puriewitsch, 

 and others a certain amount of the enzyme is present in the amyliferous 

 cells of the endosperm. 



The first visible action of diastase is seen in the starch grains of the 

 endosperm behind the upper part of the scutellum after two or three days 

 of germination at 16 C. Small central slit-like cavities and radiating 

 cracks first appear in the starch grains ; these rapidly enlarge, and 



FIG. 19. Columnar epithelium of the 

 scutellum. A, In a dormant grain ; 

 B, in a germinating grain ( x 275). 



FIG. 20. Starch grains in various 

 stages of dissolution, i and 2, 

 From a grain after 5-7 days' 

 germination ; 3, from a grain 

 almost depleted of its endo- 

 sperm ( x 575). 



dissolution proceeds also along the concentric lines of stratification. In 

 eight or ten days pits and channels are seen ; these commence on the 

 outside and penetrate into the interior of the grain, its circular outline 

 being thus broken at various points ; the grains are subsequently eroded 

 into irregular fragments, which ultimately dissolve and disappear 

 altogether (Fig. 20). 



Concurrent with the starch hydrolysis are modifications in the reserve 

 proteins of the endosperm. The protoplasmic matrix in which the starch 

 grains are imbedded expands after imbibing water, and changes into 

 a hyaline glutinous mass capable of being drawn out into long thin sticky 

 threads ; later, it loses its elastic quality and is broken down into simpler 



