24 BULLETIN 1074, U. S. DEPARTMENT OF AGRICULTURE. 
the beginning of the Christian era called the spring wheats trimes- 
trian, because they matured in three months from sowing. Linné 
(140) treated them as separate species in his Species Plantarum, 
but combined the awned factor with the spring habit in his 
species aestivum and the winter habit with the awnless factor in 
his species hybernum. Few writers have since recognized these spe- 
cies, but the placing of. both spring and winter forms of common 
_ wheat in one species, 7'ritecum vulgare, by Villars in 1787 (198) 
has been almost universally accepted. The existence of winter and 
spring forms has been recognized by most authors but has not re- 
cently been used as a character for separating species or even as an 
important character for separating varieties. The writers consider 
these distinctions to be of less value for classification purposes than 
several spike and kernel characters, when the whole country is con- 
sidered, although it is a very important separation in some areas. 
In the southern United States, both in the east and west, several 
varieties of spring wheat are fall sown, and growers do not know 
whether they have a spring wheat or a fall wheat. The Purplestraw 
variety of the Southeastern States has a true spring habit, although 
it has been grown from fall sowing in that section for more than 100 
years. Nearly all of the varieties grown in Arizona and California 
are spring wheats, but are fall sown. . 
Hunt (723, p. 54) and others have pointed out that winter and 
spring wheats can be changed from one form to the other. These 
are factors which limit the value of the characters in classification. 
To use the winter and spring habit as the first separating characters 
also would widely separate otherwise very closely related varieties 
and in practice would result in a double classification. 
The winter and spring habits are shown as the first characters in 
the descriptions, as those characters are the first apparent in the 
growth of the plant. In the key the wheats having a winter habit are 
listed before those having a spring habit, because there are more 
fall wheats than spring wheats and because fall wheat is of much 
greater importance in this country than spring wheat. 
A few varieties of winter wheat are somewhat intermediate or 
facultative in their habit of growth. This is mentioned in the de- 
scriptions of such varieties, but in the key only the two classes are 
recognized. The intermediate types retain their prostrate habit of 
growth for only a short time or else they are semierect instead of 
prostrate. Early varieties of winter wheat have a short prostrate or 
dormant period, and when spring sown they begin heading only a few 
weeks after the spring wheats have headed, thus giving an appear- 
ance of intermediate habit at the later stages of growth. There are 
