14 GROWTH AND WORK OF PLANTS 



18. Minute structure of the coats and outer layer of food 

 reservoir in corn and wheat grains. This structure is deter- 

 mined by a study of a thin section cut from a grain and extending 

 through the outer surface and a short distance into the interior or 

 flour part, and magnified by the use of the microscope. Figure 23 





'o 

 Fig. 23. 



Section through exterior part of a grain of wheat, c, cuticle, or outer layer, of bran; ep, epi- 

 dermis; m, middle layer; i, i t , layers of hull next to seed coats; s, Si, seed coats; p, layer 

 containing proteid grains; st, cells of the endosperm filled with starch. Greatly magnified. 

 After Tschirch. 



is from a wheat grain, and the parts are as follows: the outer layer 

 of cells (ep) is the epidermis, and upon this is the cuticle (c); next 

 are a few layers of cells (m) the middle layer of brown, and next 

 (i, it) comes the inner layer of brown.* Together these are some- 



the protoplasmic units are not bounded off by cell walls, still in general we 

 can say that the cell is the unit of structure, at least of the tissues of the 

 higher plants. A tissue is a group of cells of one kind, or in some cases of 

 different kinds united together. 



* These three portions of the brown layers are not a part of the seed. 

 They are a part of the fruit and are in reality the wall of the ovary inside of 

 which the seed is formed. If this brown layer could be entirely removed 

 from the grain of corn and wheat the remaining part of the grain would be 

 the seed. While then we speak of the grain of corn and wheat as seeds we 

 should remember that this usage is not technically correct, for the walls of 

 the seed capsule are consolidated with those of the seed. 



