13 
Farm Types in Nebraska 
Fig. 6. — Heat the limiting factor in border regions determined by low tem- 
1 perature. 
of heat upon farming. The crops treated as annuals are pres- 
ent in nearly every county in the United States and usually 
occupy the greater part of the cultivated land. These points 
are very essential where large-scale measurements are to be 
I made. 
While it is true that the acreage of cultivated crops 
treated as perennials is affected by heat it is also true that 
the effect of heat upon the acreage of perennials is often out- 
weighed by rainfall, soil, and economic conditions. This to- 
gether with the fact that cultivated perennials are scarcely 
represented in a large number of counties in the United States 
makes them almost useless in the measurement of what are 
, more purely heat effects. 
The census makes no attempt to keep winter, spring, and 
summer annuals separated from one another. This grouping 
of crops in the census made it necessary in some cases to use 
estimates, and in other cases supplementary data. The fol- 
lowing outline will give an idea of how the census material 
I was treated before beginning the study of heat in its relation 
