CHAPTER III 



GERMINATION OF THE GRAIN 



A NORMALLY ripened wheat grain, sown an inch or an inch and a half 

 deep in good soil, early in September, begins to germinate in two or three 

 days, the coleoptile and first leaf appearing above ground in about ten 

 days. The grain which at the time of ripening became comparatively 

 dry now absorbs water from the ground, and the dormant embryo soon 

 gives signs of growth. Concurrent with the visible morphological changes 

 in the embryo, changes occur in the reserve materials stored in the endo- 

 sperm, the solid proteins and carbohydrates of the latter being rendered 

 soluble and diffusible by the action of various enzymes. 



Before germination can proceed a number of conditions must be 

 fulfilled, the chief of which are : (i) a suitable degree of moisture of the 

 seed-bed, (2) an adequate temperature, and (3) a sufficiency of oxygen. 

 A deficiency of water, heat, or fresh air retards or completely prevents 

 germination. 



A grain which is on the point of germinating is swollen, its volume 

 compared with that of a dry caryopsis being considerably increased by 

 the water which it has absorbed. The puckered surface of the pericarp 

 covering the embryo becomes smoother, and the whole wall of the fruit 

 is tense. 



Very soon the growing embryo bursts its covering near the base of 

 the grain, the first portion to emerge being the dilated coleorhiza, which 

 expands at first in a transverse direction, and tears a longitudinal slit in 

 the pericarp, thus exposing the plumule. Just after its escape it appears 

 as a short truncate structure, falsely suggesting the presence of two rootlets 

 within it (Fig. 17), and consists of elongated and distended parenchy- 

 matous cells between which are many intercellular spaces which give the 

 tissue a white glistening appearance. Later, a number of long unicellular 

 hairs, resembling root-hairs in form and function, often arise from the cells 

 of the coleorhiza, especially near its base. 



After the coleorhiza has grown about a millimetre, the enclosed 

 primary root bores through it, usually on one side, leaving a bulging 



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