SOME HINTS ON THE MANURING OF GARDEN CROPS. 353 
The Essential Ingredients of Manures. 
In order to apply our conclusions we must next examine the effect 
on the plant and its growth of the three essential ingredients of 
manures, viz., nitrogen or ammonia, phosphates, and potash. 
Nitrogen is naturally obtained from the decay of animal and vege- 
table matter in the soil, that is, from the excreta of animals and 
from previous life, either animal or vegetable. In cultivated soils the 
chief natural source besides dung is the decay of the residues from 
previous crops, i.e., roots, stems, and leaves which are ploughed or 
dug in. Without nitrogen a soil would be absolutely sterile. 
The function of nitrogen is to build up the vascular and woody 
tissue of the straw and stem and the parenchymatous tissue of the 
leaf, or, in other words, to promote growth of stem, branch, and leaf. 
Without nitrogen a plant cannot grow ; with a sufficiency of it, it 
will grow vigorously, and if too much is given — especially in a quick- 
acting form — rapid, soft growth with long joints is produced. An 
excess of nitrogen tends to lessen fruiting and ripening, the energy of 
the plant being all turned towards growth. 
Of the manures containing a preponderance of nitrogen, which 
may therefore be calculated to promote growth, the chief are dung, 
crushed hoof, dried blood, meat meals, fish meal, feathers, rabbit's 
flick, shoddy, &c, among organic or natural manures, and sulphate 
of ammonia, nitrate of lime and nitrate of soda among inorganic or 
chemical manures. 
Phosphates are hardly less necessary than nitrogen, and from 
our present point of view perhaps the most important of the three, 
as they are present in the soil in very small quantities. Naturally 
they are derived from the disintegration of phosphate-bearing rocks, 
by which process phosphates of calcium, iron, aluminium, &c, are 
formed. Their function, roughly speaking, is the production of blossom 
and fruit. They induce a short- jointed, hard, and sturdy growth and 
promote early ripening, a growth and habit diametrically opposed 
to that encouraged by nitrogen. Phosphate has aptly been de- 
scribed as the bread-and-butter food of the plant, and in addition 
to its prime value as such it is essential to the well-being of the nitrify- 
ing bacteria on which, as already stated, we are so dependent. The 
chief phosphatic manures are those obtained from bone on the 
organic side, such as steamed bone meal, concentrated bone phos- 
phate, bone meal, dissolved bone, &c, and basic slag, ground mineral 
phosphate, and super-phosphate among minerals. 
Potash is of the three most naturally abundant, being an essential 
ingredient of most clays, in which it exists as a complicated compound 
of silica and alumina, but it is generally deficient in light soils. 
Its functions are not so clearly defined as that of the other two, 
and is therefore more difficult to explain. It plays an important 
part in the formation of the starch, sugars, essential oils, and other 
ingredients that the plant stores up in its root, stem, or tubers and in 
