20 THE WHEAT PLANT 



particular races and forms of wheat. The grains of T. aegilopoides , T. 

 dicoccoides, T. monococcum, and T. durum are almost always flinty, while 

 those of T. turgidum and many forms of T. vulgare and T. compactum are 

 especially mealy. 



Mealy grains are most commonly developed among those races and 

 forms whose individual spikelets bear the greatest number of grains, and 

 there is strong positive correlation between mealiness and high grain- 

 yielding capacity in the race of Bread wheats (T. vulgare). Varieties 

 possessing normally opaque grains are generally slow-growing wheats 

 with a long vegetative period and adapted for cultivation in humid climates 

 or on irrigated land. On the other hand, those giving a high proportion 

 of flinty grains produce less, grow and ripen more rapidly, and are met 

 with chiefly in regions having a comparatively dry continental climate. 



While some wheats maintain their distinctive type of endosperm under 

 widely different circumstances, others can be made to yield flinty or 

 mealy grains by varying the nutrition and the external conditions of 

 growth of the plant. 



The Macaroni wheats ( T. durum) have the most typically flinty grains, 

 and in these the feature is so strongly inherent that it is rarely or never 

 changed by environment. 



In the opposite class are the Rivet wheats (T. turgidum), whose grains 

 are generally opaque and mealy ; in these the character is also com- 

 paratively stable, and only with difficulty are some of them induced to 

 bear ripe, flinty grain. 



The Bread wheats (T. vulgare) are very variable in regard to the 

 physical appearance of the endosperm. While some of them exhibit a 

 strong hereditary tendency to bear grains with flinty or mealy endosperm, 

 the character is much less rigidly established in this race, and in many 

 forms of it the production of hard, translucent, or soft, opaque grains is 

 determined by climate and soil. 



Among wheats commonly cultivated in this country the flinty grains 

 of a sample when sown give rise to plants yielding either flinty or mealy 

 grains according to the season, the texture of the soil, the space allotted 

 to the plants, or their manurial treatment ; mealy grains behave in a 

 similar manner, the physical nature of the endosperm being in both cases 

 controlled by environment. 



Wheats grown in cool districts with abundant rainfall or under irriga- 

 tion have softer and more mealy grains than those cultivated in drier and 

 warmer regions. 



Voelcker's investigations at Woburn show that heavy soils have a 

 tendency to produce flinty grains, while light sandy loams give a higher 

 proportion of mealy grains, these effects being independent of the flinty 

 or mealy nature of the grain sown. 



