1 62 THE WHEAT PLANT 



In the descriptions of wheats in the succeeding chapters I have 

 adopted the following classification based on observations of more than 

 1500 forms grown for several years at Reading : 



Date of Earing. 



Very early . . . before May 24. \ 

 Early .... May 24-31. 

 Mid-season . . . June 1-7. 

 Late .... June 8-15. 

 Very late . . . after June 1 5 . 



This system of classification holds good for all districts and an early 

 or late variety will bear the same relationship to each other in regard to 

 the time of earing, wherever grown, though the actual dates to which 

 these terms correspond will depend upon the latitude and climate of the 

 place of growth. 



Early forms always have the erect habit, while late forms are prostrate 

 (see p. 69). 



Spring and Winter Wheats. At Reading, where the average minimum 

 winter temperature rarely falls below - 3 or - 4 C., I have always sown 

 all kinds of wheats in autumn and have rarely observed any damage by 

 frost, even among the most delicate kinds. 



There is, however, considerable difference among wheats in regard 

 to their resistance to frost, some being killed outright by temperatures 

 which others will withstand without damage. 



Many wheats are little injured at - 10 to - 15 C., but suffer when 

 the temperature falls much below this. 



In cold climates the differences are readily determined, and farmers 

 term the sorts which can be sown in autumn " Winter " wheats, applying 

 the term " Spring " to those which are delicate and must be sown after 

 the winter has passed. 



Varieties of T. dicoccum, T. orientate, T. durum, T. polonicum, T. 

 turgidum, and T. pyramidale are usually delicate ; on the other hand, 

 T. sphaerococcum, T. Spelta, and T. monococcum are hardy races. Some 

 forms of T. compactum and T. vulgar e are also hardy, while others are 

 tender and die out in severe continental winters. Of these, the rapid- 

 growing forms with the erect habit (p. 69) and broad leaves are usually 

 delicate, while the slower-growing, late-ripening sorts with narrow leaves 

 which lie close to the ground are hardy. 



Sinz found that Winter wheats showing great resistance to frosts 

 transpire less, have firmer tissues and higher dry-matter content than 

 Spring forms. 



I have frequently observed that hares and rabbits pick out and eat 

 typical Winter wheats before touching the Spring forms when both are 

 grown in the same field. 



