140 



THE WHEAT PLANT 



* Ripe grain from sheaves in the field. 



The volume and weight both increase until a maximum is reached 

 and then decrease ; the volume was greatest in the grains examined on 

 July 28. The water content decreased from 70 to about 50 per cent 

 during July ; at the time of cutting (August 7) the amount present 

 was 40 per cent, that in the grain taken from sheaves two to three days 

 after cutting, 15 per cent, while it was reduced to 12 per cent in the grain 

 of the crop cut and left in the field ten to twelve days. 



The dry matter increased from the beginning to the end of the develop- 

 ment and ripening of the grain. 



The weight of the individual grains also continued to increase up to 

 August 4, a few days before harvest, but rapidly fell after cutting, through 

 loss of water. 



In the week July 28 to August 4, the weight of the grain increased, 

 while the volume and water content decreased ; the migration of starch 

 and other substances into it during this period more than balanced the loss 

 of water. 



These changes in developing grains exhibit the same general pro- 

 gression each season, but investigations carried on during several years 

 show that they do not always proceed at the same rate, the loss of water 

 and the accumulation of dry matter being accelerated or retarded by 

 variations in the amount of sunlight, and the temperature and dryness 

 of the atmosphere. 



Although the ripening changes of the plant proceed gradually without 

 any definite break in continuity, four stages may be recognised, viz. the 

 milk-ripe, yellow-ripe, ripe, and dead-ripe stages. 



In the milk-ripe stage the crop has a green appearance. The lower 

 leaves of the plants are dead, but the blades of the three upper leaves, the 

 higher internodes, and the ears are living and green ; only on the edges 

 or tips of the leaves are there any visible signs of ripening in the form of 

 yellowish spots and stripes. 



