HORTICULTURAL SOILS. 



67 



will weigh only 1,000,000 lbs., or in some cases possibly even 

 less. 



The Uses of 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 

 be 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 : — 



f2 



