The Food of our Agricultural Crojjs. 
73 
general term " leguminous," which we find in more or less 
abundance in our permanent pastures, and which form part of 
our rotations. Some of these are annuals, some bi-annuals, 
some perennials ; some are grown for their seeds, some for 
fodder ; but, for whatever purpose they are grown, these plants 
possess properties which distinguish them from all others grown 
in rotation. In their stems, leaves, and seeds, they contain 
larger amounts of nitrogen than the other crops, while at the 
same time they do not respond to an application of nitrogen in 
manure, as do the other crops in a rotation. It is true, I have 
said, that under ordinary conditions of farming root crops can 
be grown without a direct application of nitrogen ; but if we 
reduce the condition of the land by the removal of one or two of 
these, it will be seen that it is impossible to grow another 
heavy crop of roots without a very liberal supply of nitrogenous 
manure. No such result follows the application of nitrogen to 
a leguminous crop. If we apply a dressing of nitrate of soda to 
a mixed crop of rye-grass and clover, we can increase the rye- 
grass to almost any extent, but not the clover. There is no 
difficulty in growing full crops of grain or roots year after year 
upon the same soil, provided we use appropriate and sufficient 
manures ; but no combination of manures has enabled us to 
grow continuous crops of red clover upon the same arable land ; 
nor have our attempts to grow continuous bean crops been 
much more successful. So uncertain, indeed, has been the 
effect obtained by the application of various artificial manures 
to this class of crops, that farmers have generally come to the 
conclusion not to manure them, but to reserve the application 
of manures to those crops which can be depended upon to pro- 
duce a profitable return. 
Although the source of the nitrogen in leguminous plants 
has been the subject of scientific inquiries since the beginning 
of the present century, it is only since the various substances 
which constitute the food of plants have been produced in a 
separate form as chemical salts, and have been applied sepa- 
rately or combined to the various crops grown in rotation, that 
the distinctive character of the leguminous crops in regard to 
the effect of nitrogenous manures has been clearly brought 
out. There is no doubt that the great influence of such a sub- 
stance as nitrate of soda upon corn crops and roots, and its want 
of effect upon leguminous crops, has led to the conclusion that 
the latter plants obtain their nitrogen from the atmosphere. 
Experiments carried out with the utmost care upon leguminous 
plants provided with abundance of mineral food only, and with 
air from which every compound of nitrogen had been extracted, 
