Iv HOW CROPS GROW. 
subject of vegetable nutrition, and to estimate accurately 
how and to what extent the crop depends upon the at- 
mosphere on the one hand, and the soil on the other, for 
the elements of its growth. . 
It has been sought to present the subject inductively, 
to collate and compare, as far as possible, ad the facts, and 
so to describe and discuss the methods of investigation 
that the conclusions given shall not rest on any individual 
authority, but that the student may be able to judge him- 
self of their validity and importance. In many cases ful- 
ness of detail has been employed, from a conviction that 
an acquaintance with the sources of information, and with 
the processes by which a problem is attacked and truth ar- 
rived at, is a necessary part of the education of those who 
are hereafter to be of service in the advancement of agri- 
culture. The Agricultural Schools that are coming into 
operation should do more than instruct in the general re- 
sults of Agricultural Science. They should teach the 
subject so thoroughly that the learner may comprehend 
at once the deficiencies and the possibilities of our knowl- 
edge. Thus we may hope that a company of capable in- 
vestigators may be raised up, from whose efforts the 
science and the art may receive new and continual im- 
pulses. 
In preparing the ensuing pages the writer has kept his eye 
steadily fixed upon the practical aspects of the subject. A 
multitude of interesting details have been omitted for the 
sake of comprising within a reasonable space that informa- 
tion which may most immediately serve the agriculturist. 
It must not, however, be forgotten, that a valuable principle 
is often arrived at from the study of facts, which, consid- 
ered singly, have no visible connection with a practical 
result. Statements are made which may appear far more 
curious than useful, and that have, at present, a simply 
speculative interest, no mode being apparent by which the 
farmer can increase his crops or diminish his labors by help 
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ee 
