HORTICULTURAL SOILS. 
67 
will weigh only 1,000,000 lbs., or in some cases possibly even 
less. 
The Uses op Soil. 
The uses of a soil to plants are to provide a firm yet sufficiently 
deep and porous layer, into which the roots can penetrate, and 
extend their fibrils and rootlets in every direction. The soil 
has to support the plant in an upright position, and keep it 
firm, when in the open air, against the storms of wind and rain. 
It must allow of the free percolation of both water and air, 
which are so necessary to the life and growth of the plant, and 
to the due preparation of plant-food in the soil. It must retain 
sufficient moisture to furnish the growing crop with an 
immediate supply of water, and its pores must be sufficiently 
fine to allow of the ascent of water from the subsoil by capillary 
attraction. It must store up some of the heat received from the 
sun in the day-time, and so render the temperature of the soil 
more equable. It also serves as a protective covering to roots 
and seeds against excessive summer heat and winter frosts. 
A soil should contain in itself a stock of the mineral food 
necessary to the growth of crops, and it must constitute the 
laboratory of a number of wonderful actions whereby plant- 
food is always being prepared little by little for reception and 
assimilation into the plant. For a soil to be fertile it must 
permit of the various tillage operations by which alone the 
surface can be kept free from weeds, and given the proper 
conditions of texture necessary for the sowing of different 
seeds, and for the healthy development of the various crops 
grown upon it. 
All fertile soils are made up more or less of each of the 
following substances:—Gravel, clay, sand, carbonate of lime 
(chalk), and vegetable matter. Each of these ingredients can 
he discovered in, and separated from, a soil by simple means. 
The proportions in which they are mixed together in any given 
soil have great influence on the uses to which the soil can be 
put in practical horticulture, and the kind of crops and in¬ 
dividual plants best fitted for it to grow. 
Table II. gives an illustration of the mechanical analysis of 
five different descriptions of soil, cut to 9 inches deep. The 
quantities are quoted in 100 lbs. of each, free from moisture :— 
