188 
manures for the purpose of adding to the fertility of the soil or 
restoring the elements of plant food extracted from it by the crop. 
The science of agricultural chemistry has thrown such light on 
the question of fertilisers and in the study of the requirements of 
cultivated plants that we are now able, with a certain amount of 
certainty, for every pound spent in suitable manures to expect a 
good return. 
Few soils can do without manure of some sort in order to yield 
a maximum crop. Occasionally some are, if anything, too 
rich and too forcing for the purpose of fruit-growing; they induce 
an extravagant growth of leaves and wood to the detriment of the 
fruit. Wine grapes on such soils produce a thin must of little value 
for the purpose of wine-making as compared with must from similar 
grapes grown on poorer ground. 
Most soils respond liberally to the application of suitable 
manures, and in order to satisfy the requirements of the crops en- 
trusted to them, some knowledge of what is plant food and how 
plants feed must necessarily prove helpful. 
WHat is Puant Foon. 
Plants, in order to live and fructify, require certain elements 
of food, fourteen in number, some of which are supplied by the aur, 
and some are found in the soil. Those supplied from the air are 
combinations and compounds of carbon, hydrogen, and oxygen; 
they constitute, with the compounds of nitrogen and sulphur, which 
are drawn from the soil, the organic part of the plant, which on 
combustion, either by fire, fermentation or putrefaction, return 
entirely or partly to the air. The mineral part of the plant which 
is represented by the ashes left behind after complete combustion 
constitute the inorganic constituents; they consist of potassium, 
phosphorus, calcium, magnesium, iron, silicon, sulphur, sodium, 
chlorine, and manganese. 
Some knowledge of the composition of the tissues of plants and 
fruits will be useful for understanding in what proportion the 
different elements indispensable for plant growth occur in most 
crops. 
Nearly two-thirds consist of water which disappears on desic- 
cation, and the balance is made up mostly of combustible organic 
matter (carbo-hydrates), such as fibre, starch, sugar, gum, oils, 
alkaloids, and albuminoids, gluten, albumen, ete.; and also one to 
three per cent. of mineral or inorganic matters represented hv the 
ashes. 
To agricultural chemistry and such works as those of Wolff, in 
Europe, and Professor Hilgard, of the University of California, we 
