HORTICULTURAL SOILS. 
69 
that fall victims to organic law. We have to remember, further, 
that the greater part of the weight of every plant is obtained 
from the air, and only a very little is derived from the soil. 
Not only so, but it is a fact, and a very important one, that new 
plants grow much more quickly than the remains of the old 
ones decay and disappear; hence organic carbonaceous matter 
must always be increasing in a soil left in a state of nature and 
uncultivated. 
The character and amount of plant-growth is found to differ 
considerably in different soils, and the largest quantity of 
produce will be grown on the soils where the wild plants could 
get the greatest amount of food. It happens, therefore, that the 
virgin soils, as they are termed, derived from the heath, the 
forest, or the prairie, which are first ploughed up by the settlers 
in new countries, are richly charged with a blackish-brown 
vegetable substance, known under the general name of humus, 
and recognised as one of the marks of a fertile soil. In fact, 
humus was considered by agricultural chemists in the early part 
of the present century to be the main source of soil fertility. 
But without supposing that plants feed directly upon humic 
matter, it is easy to see why the proportion of this substance is 
often a very fair measure of the productiveness of a soil, for the 
reason that it represents the material accumulated by a previous 
succession of crops. 
Table III. shows the proportion of organic matter, and of 
nitrogen in the organic matter, in seven descriptions of soil, in 
quantities per acre, the soil being cut to 9 inches deep. 
TABLE III. —Organic Matter and Nitrogen in Different Descriptions 
of Soil per acre, cut to 9 inches deep. 
Description of soil 
Organic matter 
Nitrogen 
lbs. 
lbs. 
Arable loamy soil . 
34,500 
3,360 
Pasture soil .... 
76,050 
5,558 
Prairie soil .... 
117,225 
9,630 
Forest mould .... 
126,900 
6,750 
Leaf mould .... 
141,950 
8,805 
Peat mould .... 
188,000 
5,000 
Heath mould (Ghent) 
640,000 
11,650 
The figures show a very considerable range in the amount of 
