PHYSIOLOGICAL PROCESSES DURING FLOWERING 443 



germination. Readily soluble and mobile substances, chiefly 

 hexoses and amino acids, are transported toward the seeds and 

 are transformed there into insoluble or almost insoluble sub- 

 stances of a high molecular weight, such as starch, fats, and 

 proteins. The dry weight of ripening seeds increases rapidly. 

 The water content, on the contrary, decreases continually. 

 Toward the end of ripening, the loss in water may exceed i\w 

 accumulation of dry substance and the weight of the seeds 

 may even decrease. Novacky (1870) observed the following 

 changes in the weight of ripening seeds of wheat in grams per 

 100 seeds. 



Stage of development 



Beginning of the milk stage 



End of the milk stage 



Dough stage 



Completely ripe 



Total 

 weight 



5.89 

 7.23 

 5.65 

 4.59 



Dry 



weight 



2.86 

 3.58 

 4.19 

 4.22 



Water 



3.. 03 

 3.65 

 1.46 

 0.37 



The general changes in accumulation of the various substances 

 in the wheat grain are presented in the following diagram (Fig. 

 138) taken from the work of Thatcher (1913). 



In starchy seeds, the synthesis of this storage carbohydrate 

 from monosaccharides proceeds very rapidly; and therefore, even 

 in the early stages of development, the sugar content of ripening 

 seeds does not exceed 1 or 2 per cent. In oily seeds, the metabo- 

 lism of carbohydrates into fats is more complicated. Very often 

 in the early stages of ripening there are found in these seeds not 

 only monosaccharides, but even starch, which are gradually 

 transformed up to the time of complete ripeness into fats. 

 Leclerc du Sablon observed the follow^ing changes in the content 

 of different substances of the walnut. On July 6, the seeds 

 contained 3 per cent of oil, 7.6 per cent of sugars, and 21.8 per 

 cent of starch and dextrin. On August 1, the oil content rose 

 to 16 per cent, while the sugar content fell to 2.9 per cent and 

 that of starch of 14.5 per cent. At the time of complete ripeness, 

 October 4, the oil content increased to 62 per cent, while the 

 sugar content fell to 1.5 per cent and that of starch to 2.6 per 

 cent. 



