MORPHOLOGY OF THE r.AU.KY GRAIff. 
1 
character of the aleurone sheath. The first starch grains are formed 
in the older ureas of the endosperm near the distal cud of the grain. 
According to Brenchley, 1 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 furrow are affected much later and to a lesser degree. As above 
stated, the aleurone layer begins to differentiate soon after the embryo 
^ac becomes filled with new cells. It consists at first of a single 
layer, increased to three 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. Their contents quickly show the 
characteristic aleurone nature. The dense mass of glutinous and 
fatty 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 
perforated with small 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 
becomes 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 entirely justified, in that, although numerous endosperm cells 
are emptied of their contents and a mass of collapsed cell walls is 
crowded before the 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 the starch is effected by 
the processes typical of the diastase of translocation rather than by 
that of the corrosive action of digestion. 
i Brenchley, W. E. Development of the grain of barley. Annals of Botany, v. 26, no. 103, p. 903-928, 
22 fig., 1912. 
