478 



DIGESTION 



have been shown to secrete proteinases into the liquid in the "pitcher" or, 

 in the sundews, on the surface of the leaf. 



Certain tissues of the embryo in the grains of various members of the 

 grass family also produce exoenzymes (Brown and Escombe, i8g8, and 

 others). This phenomenon cannot be appreciated without a knowledge of 

 the various parts of the grain type of fruit. These are illustrated in Fig. 

 103 which represents a longitudinal section cut through a corn grain across 

 the shorter of the two transverse axes. The structure of the other grains 



^pericarp 

 endosperm 

 5cai-ellum 



coleopi'i/e 

 plumule 



coleorhiza 

 pr/mary roof 

 roo^ cap 



)scufellum 



== [endosp&rm 



Fig. 104. Section through a small por- 



FiG. 103. Longitudinal section through tion of a germinating corn (maize) grain. 



a corn (maize) grain to show principal Starch has been digested in several layers 



parts of grain and embryo. of endosperm cells adjacent to the scutellum. 



(wheat, barley, rye, etc.) is, in general, very similar to that of the corn 

 grain. 



Shortly after a grain of corn, barley, or one of the other closely related 

 species begins to imbibe water striking changes take place in the appearance 

 of the epithelial cells of the scutellum (Fig. 104). The protoplasmic con- 

 tents of these cells, originally finely granulated and nearly transparent, be- 

 come much coarser in texture and clouded in appearance. The nucleus, 

 originally clearly visible, is obscured by this change in the physical properties 



