96 



BOTANY OF CROP PLANTS 



Embryo. — In the very young stage, prior to fertilization, 

 the axis of the ovule is parallel with that of the ovary. Soon 

 in its development, the ovule turns so that its micropyle is 

 directed downward (Fig. 33). At first, the young ovule 

 does not fill the ovary cavity, but soon does so by further 

 growth. The ovule is attached along its side to the ovary. 

 The groove indicates the position and extent of this at- 

 tachment. The first pair of seminal 

 (seed) rootlets appears in the embryo 

 about four weeks after pollination. 

 About a week later, two other rootlets 

 appear above the first pair, and 

 Brenchley describes a fifth lateral 

 rootlet, which does not appear until 

 quite late. 



Endosperm. — In about a week or ten 

 days after fertilization, a definite tissue 

 is formed within the embryo sac. This 

 is the endosperm. About seven or 

 eight days later, the aleurone layer is 

 marked off, appearing first on the dorsal 

 side. According to Brenchley, starch 

 first begins to appear in the "flank" 

 cells about the eleventh day after pollination. Eckerson 

 points out that the actual time of the beginning of deposi- 

 tion depends upon the relative activity of the leaves in 

 making sugar and of the embryo in assimilating it. 

 Infiltration of starch is complete in about five weeks 

 after pollination. It is held that reserve nitrogenous 

 matter enters the endosperm at the same time as the 

 starch. 



Grain Coats. — Before fertiUzation," the grain coats are as 

 follows : 



wote- 



micropijle' 



Fig. 33. — Diagram- 

 matic section o£ young 

 ovary of wheat. (After 

 Bessey.) 



