PART III.—STATISTICAL FARM WORK. 
Chapter XIII. 
THE CROPS AND CLIMATES OF THE UNITED STATES. 
The ultimate object of our inquiry is to determine the exact per- 
centage of the effect of normal and abnormal climates upon special 
crops in special regions of this country and the relation to the whole 
crop of the United States. To this end we must first ascertain the 
climatic effect on the yield per acre, and this is our present special 
problem, leaving it to the statistician and census taker to ascertain 
how many acres are under cultivation and what the actual effect will 
be in bushels or pounds. The climatologist, or Weather Bureau, 
has only to determine numerically the climatic effect upon a given 
unit area. 
The tables of yield per acre for ten important crops and for all 
years will be given in a subsequent portion of this section, but the 
study of these must be preceded by several studies into matters that 
are not strictly climatic, but which nevertheless enter into the statis- 
tics of actual harvests and obscure the strictly climatic influences. 
Thus the statistics must be corrected in some way for the effect of the 
customary modes of cultivation and the quantity of seed that is sown, 
on which point I give statistics appropriate to the United States. 
Again, before comparing our climatic data with the phenomena of 
vegetation we must know something of the average date of seeding, 
with respect to which I have given the dates for seeding of winter 
wheat. 
The corresponding dates for rye will not differ very much. The 
dates for maize, potatoes, tobacco, and cotton have already been given 
for special localities, but still require to be tabulated in a general way. 
The necessary climatic data are given in my next section for twenty 
Signal Service stations, and I regret that the shortness of time has 
not allowed me to give more complete data for these and for all other 
stations, but the tables here presented will serve to show the form in 
which such data should be presented for the greatest convenience 1n 
phenological studies. 
But before entering upon so extensive a system of numerical com- 
parisons it is necessary to bear in mind certain principles which I 
would illustrate in the following remarks. 
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