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VARIABILITY OF RESULTS FROM PLAT EXPERIMENTS. 
The reliability of the data obtained from experiments on small 
plats of ground, and on which we should naturally place much reli- 
ance in discussing the relation between climates and crops, is a matter 
of the first importance, and we must begin our study with an attempt 
to obtain a clear idea as to the extent to which such data are fit to be 
used as a basis for our studies. In the hght of all that has thus far 
been ascertained with reference to the nature of the influences at work 
to increase or diminish the resulting crop, we may safely say that the 
results obtained from two different plats will not be comparable with 
cach other and still less be applicable to the larger fields harvested 
by the farmers, unless we know for each plat or field the absolute or 
relative conditions as to the following matters: 
(1) The mechanical condition of the soil as affecting aeration, per- 
colation, and temperature. 
(2) The chemical nature of the original soil. 
(3) The character, proportion, and uniformity of distribution of 
the fertilizers and the history of the previous rotations of crops on 
these plats; the influence of climate, rain, and drainage on the avail- 
able nutrition in the soil. 
(4) The dates of cultivation and application of the fertilizers. 
(5) -The exact area of the plats. 
(6) The distance apart of the hills or stalks. 
(7) The number and quality of seeds sown per acre. 
(8) The moisture in the soil at the beginning and the quantity 
and times of rain or irrigation. 
(9) The chemical and biological quality of the rain or irrigation 
water—i. e., rain or snow water; rain with much or little nitrogenous 
compounds and biological germs. 
(10) The injury by insects and animals. 
(11) The temperature of the soil. 
(12) The remaining climatic details as to heat, sunshine, dryness, 
and velocity of the wind. f 
(13) The sterility of the soil as to the microbic life that seems 
indispensable to the success of certain crops or to the growth of the 
plants. 
(14) The nature of the climate in which the seed and its immediate 
ancestor was grown. 
In the total absence of knowledge as to many of these points and 
fragmentary knowledge on others, a simple direct comparison 
between the results of two plats lying side by side and that have in 
some few respects been treated alike must be entirely misleading. 
But the extent to which such comparisons are deceptive, or rather the 
