98 



BOTANY OF CROP PLANTS 



In the milk-ripe or green-ripe stage, the embryo is already 

 fully developed. The grain changes from pale green to dark 

 green in color, which change Nowacki explains as being due 

 to the resorption of several layers of the ovary wall, through 

 which the chlorophyll layer now shows. The endosperm cells 

 are filled with a watery sap in which are suspended a number 

 of starch grains; hence, when the grain is squeezed a white, 

 milky juice comes out. 



In the yellow-ripe, gold-ripe, or "dough" stage, the cells 

 of the ovary wall become thicker. The lumina of inner in- 

 tegument cells decrease in size, due to an increase in the 

 thickness of their walls. The color of the grain changes 

 from green to yellow, and the endosperm becomes tough and 

 waxy. 



The full-ripe stage follows close upon the preceding. As a 

 result of water loss, the different cell layers become dis- 

 torted. The grain becomes harder and firmer. Grain is 

 usually harvested while in this stage. 



If the crop is now left in the field, the grain becomes brittle; 

 it is then said to be in the dead-ripe stage. 



Nowacki gives the following analyses of grains of wheat at 

 different stages of development: 



Water content 

 of grain 



Dry substance 



in 100 grains, 



grams 



Milk-ripe (a) July 9 

 Milk-ripe (6) July 13 



Yellow-ripe 



Full-ripe 



The maturity of the grain appears to affect its vitality. 

 Kedzie has shown that wheat collected in the dough stage 



