65 6 
FOOD OF PLANTS. 
has been supplied to the roots without the least apparent ad¬ 
vantage. If it could be applied in the form accessible to the 
roots of plants, it is not known that it would pass through 
the elaborations and combinations in the plant, and ultimately 
constitute charcoal in the organization. The case of an 
animal shows that whatever kind of common food is consumed, 
the necessary parts are formed; and it may be supposed that 
plants have similar power of producing the necessary con¬ 
stituent parts from various substances both dissimilar to each 
other and to the materials that form the composition of the 
plant. Of elastic matters there may ever be little or no 
control; they are generated by causes much beyond command 
or application; and of the solid substances that are applied as 
manures, it is not known what part, or if any part of them, 
passes into the plant as nourishment, what agencies they and 
the soil exert over each other, and what combinations they 
enter into with the atmosphere, by which they ultimately 
become so highly conducive to the growth of plants. 
The expectation of gaining any knowledge of the matters 
which form the food of plants, and of a mode of applying 
those matters to the soil, from an investigation of the con¬ 
stituent parts of the plants themselves, must rest on a very 
uncertain supposition ; for in any case of similarity or analogy 
that exists in the natural v T orld, no deduction of that kind can 
be made, and from observation and experience all the knowledge 
that is possessed on these subjects has been derived. If the 
veil were withdrawn with which nature has enshrouded many 
of her w orks beyond the reach of our visual organs, and our 
eyes were permitted to roam over a field very probably for 
ever and very justly forbidden to man, the probability is that 
our practice might not be any way improved thereby. On the 
contrary, the attention might be diverted from principles that 
never fail, and wander in pursuit of an Utopia, probably never 
to be obtained by our utmost scientific research, or reduced to 
practice by any human skill. But on the other hand, it is 
very possible to use any advantages that may result from such 
investigations, without departing in any hurtful degree from 
the solid principles of practice. The combination of science 
with practice, so far as the former is capable of application, 
will ever constitute the safe mode of proceeding with every 
judicious cultivator, ever bearing in mind, and never for a 
moment forgetting, the influence of physical causes and of ex¬ 
ternal agencies that bear on every such application, on which 
the whole matter hinges, which are generally overlooked, and 
over which human agency never can exert any control. From 
want of a due attention to the different circumstances of 
