Mar. i 7 , i9*3 Influence of Soil Temperature on Seedling-Blight 849 
growing tip from contact with the soil or soil-inhabiting organisms. At 
8°, for instance, the coleoptile usually was 2 to 4 cm. above the surface 
of the soil before the first leaf pushed through. This variation in type 
of emergence may help explain the protective influences of low soil 
temperatures against certain diseases of the small grains. 
The largest top production during the early seedling stage was at 20° 
to 2 4 0 C. As the plant increased in age there was a gradual lowering of 
the optimum temperature for development of tops, until in the later 
stages of development the best top development resulted at 12 0 to 16 0 . 
The rate and extent of tillering of spring wheat was modified at the 
extremes of soil temperature, both high and low. The plants tillered 
first at the temperatures producing most rapid emergence, namely 24 0 
to 28° C., which indicated somewhat similar cardinal temperatures at 
this stage of development. Only a limited number of tillers formed at 
32 0 and above. Below this, soil temperature had little effect on tillering 
until at 8°, where the tillering was limited to two or three culms per plant. 
The maturation of the wheat plant was hastened by low soil temperatures. 
Hutcheson and Quantz ( 19 ) and Appel and Gassner (2) have shown this 
to be true for several of the small grains. The plants grown continuously 
at a soil temperature of 16 0 were the first to head and mature. The time 
of maturation increased slightly with variation in each direction, the 
plants at 8° maturing at approximately the same time as those at 24 0 . 
At temperatures of 24 0 and above, the heading was retarded very con¬ 
siderably, intemodal elongation was reduced, and leaf production stimu¬ 
lated, the spring-wheat plants at 28° heading when only 10 to 12 inches 
high. Heading was almost entirely inhibited at 32 0 and above, regardless 
of the season of the year. 
While spring wheat germinated more rapidly at soil temperatures of 24 0 
to 28° C., the germination was more uniform and stronger plants resulted 
at the lower temperatures—about 8° to 16 0 . The greatest development 
of roots as well as of tops occurred at the lower soil temperatures. The 
earliest maturing, most stocky, and best filled plants resulted at soil 
temperatures of about 16 0 . 
INFLUENCE OF SOIL TEMPERATURE ON THE DEVELOPMENT OF TURKEY 
WHEAT 
The cardinal temperatures for the development of Turkey winter wheat 
were, in general, about 4 0 C. below those for spring wheat. The responses 
were very similar, except that winter wheat tillered excessively at soil 
temperatures of 24 0 and above, and maturation was inhibited by this 
and higher soil temperatures. Plants grown continuously at soil tem¬ 
peratures of 28° and above were not only checked in their intemodal 
elongation, but failed to form even the embryonic floral organs, the leafy 
vegetative development continuing throughout the season. Chemical 
analyses showed this to be a carbohydrate nitrogen balance similar to 
that described by Kraus and Kraybill {23) in the tomato. The analytical 
data will be discussed in detail in a later paper. 
INFLUENCE OF SOIL TEMPERATURE ON THE DEVELOPMENT OF CORN 
Disease-free, uniformly matured com was selected for all the tem¬ 
perature experiments. Usually the seed for the entire series of experi¬ 
ments was taken from a single ear. The com was planted 1.5 inches 
