THE FOOD OF PLANTS. 
57 
albumen, oil, &c., are built up from inorganic compounds. But 
there are several ways of learning with certainty not only what 
elements are essential to a plant, but also in what form of com- 
bination the several elements must be supplied. One may learn 
much concerning these points by studying the constituents of 
fertile and sterile soils, or by the chemical analysis of the plant 
itself; or by an examination of the final products of decay into which 
animals are resolved after death ; or by experiments tried on 
plants ; or even by careful scrutiny of the constituent elements 
of animals and animal secretions. By such means, then, but 
especially by the chemical pulling to pieces or analysing of 
plants, has much information been obtained as to the elements 
invariably found in all plants, and concerning those occasionally 
occurring in particular orders, genera, or species. We will en- 
deavour in the present paper to give an outline of the chief facts 
concerning the food of plants, filling in here and there, for pur- 
poses of illustration, some of the minuter details which careful 
chemical investigations have revealed. 
Plants connect the mineral with the animal kingdom, and 
without plants animals could not exist. Looking at this con- 
nection in its broadest features, omitting details and exceptional 
or reverse actions, 
we may express in 
a simple diagram- 
matic sketch the re- 
lations of the three 
kingdoms of na- 
ture. Let the cycle 
of changes be re- 
presented by alarge 
circle, and let the 
several spheres of 
chemical substan- 
ces and chemi- 
cal changes, mine- 
ral, vegetable, and 
animal, be repre- 
sented by smaller 
circles, epochs or 
stages, as it were, 
in the system, with the sun as its centre, then we have a plan 
like this. 
Here we see how mineral substances nourish the plant, and 
are transformed into vegetable tissues and products; how the 
plant feeds the animal, being ti;ansformed into its flesh and bones ; 
and how, as the last step in this perpetual circulation of matter, 
the animal after death relapses once more into purely inorganic 
