MORPHOLOGY OF THE BARLEY GRAIK. 7 



cliaracter of the aleurone sheath. The first starch grams are fonned 

 in the older areas of the endosperm near the distal end of the grain. 

 Accordmg to Brenchley/ this occurs on the sixth day after flowering 

 and in the middle of the flanks of the grain. On the seventh day, 

 scattering grains are apparent in two-thirds of the length of the grain. 

 On the tenth day, the deposit is very heavy in the flanks and extends 

 almost to the embryo. It is not until the nineteenth day that the 

 main body of the starch is completed. The cells next to the aleurone 

 layer are the last of the endosperm tissue to fill with starch. 



Accompanying this infiltration of starch are certain modifications 

 of the nuclei of the endosperm. Just before the first starch grains 

 are formed the nuclei become granular. For a time they are full of 

 vigor, with the starch grains arranged about them. As the process 

 advances, the nuclei gradually become distorted by pressure exerted 

 by the growing starch. The cells next the aleurone layer and near 

 the fuiTow are affected much later and to a lesser degree. As above 

 stated, the aleurone layer begins to differentiate soon after the embryo 

 sac becomes filled with new cells. It consists at first of a single 

 layer, increased to tliree as the endosperm mass grows. The cells 

 are arranged radially and present about the same appearance in 

 both cross and longitudinal section. In tangential section their 

 arrangement is very irregular. Theh contents quickly show the 

 characteristic aleurone nature. The dense mass of glutinous and 

 fatt}' compounds, the aleurone grains themselves, and the large 

 nuclei are present in no other section of the endosperm. As the cells 

 approach maturity the walls become very thick and are seen to be 

 pei-f orated with smaU canals. 



It is only after the cells of the endosperm have divided many 

 times and the endosperm mass is beginning to take shape that the 

 embryo begins active development. At first it lies free in the sap 

 at the lower end of the embryo sac. Gradually the endosperm 

 })ecom('S organized about it, and by the time the more prominent 

 divisions of the embryo have become differentiated the two are in 

 contact. The later growth of the embryo is at the expense of the 

 starch endosperm and during germination their relation is that of 

 parasite to host; but before the grain is matured this statement is 

 not entindy justified, in that, although numerous endosperm cells 

 are emptied of their contents and a mass of collapsed cell walls is 

 crowded before tlu^ upper angle of the scutellum, their reduction 

 takes place more in the; manner of normal growth. The cell walls 

 are not broken down, and the removal of tiie starch is effected by 

 the processes typical of the diastase of translocation rather than by 

 that of the corrosive action of digestion. 



1 lirerichley, W, E. Development of the grain of barley. Annals of Botany, v. 20, no. 103, p. 90:j-928, 

 22 ng., 1912. 



