CLASSIFICATION OF AMERICAN WHEAT VARIETIES. 25 



also certain varieties of wheat which are not homozygous as to winter 

 or spring habit. The habit of growth is determined by sowing the 

 wheat in the spring and observing its behavior. A winter wheat is 

 one which usually produces no seed when sown at the normal date of 

 seeding for spring wheat. All varieties classed as winter wheats in the 

 key can be successfully produced only from fall sowing. When spring 

 sown they usually remain prostrate on the ground throughout the 

 growing season and produce no culms or spikes. In some sections, 

 or in some years, or when sown very early, winter-wheat varieties 

 when spring sown will head and produce seed, but this usually occurs 

 very late in the season. 



All varieties of wheat classified as spring wheats can be success- 

 fully grown from fall sowing only in mild climates, such as the 

 southern parts of the United States and along the Pacific coast. In 

 parts of this territory they will sometimes winterkill. When spring 

 sown their early growth is erect and culms and spikes are produced 

 during the early part of the growing season. 



TIME OF MATUEITY. 



The time between emergence and maturity is often an important 

 economic factor in wheat production. The duration of the growing 

 period is indicated by classing varieties as early or midseason or late. 

 These are considered secondary characters, but nevertheless are im- 

 portant economically and also in classification. Winter wheats and 

 spring wheats require periods for growth which can not be directly 

 compared in number of days. Fall-sown spring wheats may mature 

 as late as or later than many of the true winter wheats. The above 

 separation, however, into three classes can be used for both fall and 

 spring wheats, or for all wheats when sown in the fall. No definite 

 unit of time is used, therefore, in defining these separations. It is 

 simply a relative measurement to be used in comparing varieties with 

 those of which the normal time of maturity is known. Spring 

 varieties grown in the northern Great Plains area would be classi- 

 fied as early when maturing in 85 to 95 days after emergence, as mid- 

 season when maturing in 90 to 100 days, and as late when maturing 

 in 95 to 105 days. These variations are so small and such differences 

 between the varieties are apparent during so short a period that these 

 factors are of minor value in classification and are used only to 

 separate closely related varieties. 



TILLERING. 



The tillering or stooling of wheat also is of little taxonomic value 

 in separating varieties. Koernicke and Werner (133) recorded the 

 number of plants and culms obtained from definite quantities of seed. 



