MANURES AND THEIR USES, 
201 
MANURES AND THEIR USES. 
By Mr. Wm. Geo, Watson. 
[Bead September 10, 1895.] 
Plant Food. 
If abundant and invigorating food bo given to an animal it 
increases in weight and fatness, whereas on a scanty and poor 
diet it continues thin and weakly. It is precisely the same with 
plants. If they find in the soil all the substances which they 
require, in sufficient quantity and in suitable form, they will 
grow more vigorously and produce better crops than when they 
meet with those substances (or, perhaps, even only one of them) 
in insufficient quantity. Every soil not absolutely barren is 
capable of bearing plants. Left to itself it would soon become 
clothed with vegetation. "Even when the soil is covered deeply 
with water it does not cease to be a dwelling-place for plants 
although these are of a different organisation from the plants 
growing upon the surface of the land. Plants, like animals, 
must obtain nourishment, and in order that a plant may live 
and grow it is necessary that its four organic constituents — 
carbon, hydrogen, oxygen, and nitrogen — should be absorbed by 
it ; and that this absorption may take place, it is essential that 
they should be presented to the plant in a suitable form. 
Plants obtain the elements of which they are built up partly 
from the atmosphere and partly from the soil. Ninety-five per 
cent, of all the substances found in plants is obtained from the 
atmosphere, and the increase of the earth's produce is due more 
to the help of Nature than to the skill of man ; but the 5 per 
cent, obtained by the plant from sources other than the atmo- 
sphere is just as necessary to the growth of the plant as is the 
other 95 per cent., for without it neither the oxygen, hydrogen, 
carbon, or nitrogen could be assimilated. 
All fertile soils contain organic and inorganic matters, and 
every plant, in like manner, is made up of an organic and an 
inorganic part. Carbon, oxygen, hydrogen, and nitrogen are 
found in all plants and animals, and are called the organic 
elements. 
