8 



properly cooked plant food. It will be seen from this that the similarity between the chemical con- 

 stituents of a soil and the ashes of a green plant cannot be accepted as a criterion of its suitability for 

 the growth of that plant, and that tables professing to guide the farmer by means of such comparisons 

 are misleading. Again, some plants are surface feeders, and others draw their supplies from far be- 

 neath the surface. Others have their roots formed to penetrate the interstices of stony ground, and 

 others to push their rootlets through stiff soil ; and no temptation in the shape of chemical constituents 

 approximating to their ashes will induce them to alter their predilections in these respects. The theory 

 so brilliantly expounded by the great agricultural chemist, Baron von Liebig, that the adaptability of 

 a soil for a given plant depended on the similarity between the often minute mineral constituents of 

 one and the ash constituents of the other, is now thoroughly exploded in Europe under the crucial test 

 of extended practical experiment ; and I was not a little surprised to find that a large measure of cre- 

 dence is still extended to it in these colonies. Consequent upon the proportions which the clay, sand, 

 chalk, and humus occupy in the soil, it possesses — 



1. Permeability to water, &c. ; power of absorbing and retaining moisture. 



2. Power of absorbing and retaining plant foods in gaseous uud liquid forms. 



3. Colour. 



The permeability of soils to water is of great importance, and many soils apparently similar will be 

 found to differ largely in this respect Fill a number of tubes of one inch in diameter, having the 

 lower end closed by muslin, with soils of different samples ; stand the tubes upright ; and gently pour 

 on water, filling the tube to a certain distance above the soil. It will be found that in some soils the 

 surface will always be dry long before others. That soil which has its surface so >nest dry, while hold- 

 ing relatively by weight the greatest quantity of water in its pores, is, all things being equal, the most 

 fertile soil. Thus the surface of poor sand will soon be dry, but the water will all have run through, 

 and little relative increase in weight will be recorded, while with an equally unproductive clay the 

 surface will not be dry for a long time, though the weight will be increased considerably. The follow- 

 ing table of the comparative absorptive powers of soils is taken from Schubler, and will be useful in 

 this connection — 









Of 100 parts of water 







Water absorbed by 



absorbed, there evapo- 1 







100 parts. Per cent. 

 . 



rate in four hours, 

 at 66° F. 





Sand 



25 



88.4 





Light clay 



40 



52.0 





Stiff clay 



50 



45.7 





Heavy clay 



61 



34.9 





Pure clay 



70 



31.3 





Humus 



190 



20.5 





Rich garden soil 



96 



24.5 



From these figures it will be seen that the richer a soil is in decaying vegetable matter the more 

 rapidly and extensively it will absorb water, while the more slowly it will part with it. This is 

 not only true as regards the water which falls upon a soil in the shape of rain, but also of the 

 moisture deposited in the shape of dew and absorbed by the soil from contact with damp 

 air. The power of absorbing and retaining plant food in gaseous and liquid form is another 

 peculiar property which they possess. This property was well illustrated at Merthyr Tydvil when 

 the sewage of that town was poured on to an area of sandy loam, with the result that the water came 

 through quite clear and entirely deprived of the matters — chiefly plant foods in soluble form — which 

 it had held in solution on suspension. This important property is much more active in soils possessing 

 a fair degree of humus in its composition, and it is also markedly more active in soils which are 

 porous, and soils which are well worked will absorb from the water which passes through them far 

 more plant food in a fit condition for the immediate needs of the plant than those which are allowed 

 to remain unfilled, and this is one great reason why the surface of soils should be continually stirred 

 and exposed to the air, from which it absorbs no small part of its supply of plant food. I have divided 

 the plants in a large conservatory into two equal classes, of equal numbers, and in about equal states 

 of health. I had the surface of the earth in the pots of one class continually stirred, and the surface 

 in the other pots left untouched for four months during the growing season. The result was a most 

 marked increase in growth and improvement in health on the part of those plants which had the sur- 

 face of the soil around them constantly stirred. 



The colour and texture of soil have a great effect upon their fertility by the absorption of heat. 

 Black humus soils absorb heat far more readily than those of a lighter colour, and the heat penetrates 

 to a greater depth. Anyone can try this for themselves by sowing two boxes of seed, one in light- 

 coloured and the other in dark-coloured soil. He will find that the latter will germinate a compara- 

 tively long time before the former. 



Plants derive from the soil the mineral constituents which compose their ash, and it is in the 

 determination of the presence, or otherwise, of the mineral constituent that the chemist can aid the 

 farmer after the latter had either chosen his soil with a due regard to its physical qualities, or, by means 

 of judicious admixture with other soils, has brought it to a state of loam and has so improved the sub- 

 soil as to secure the essential free drainage. The following methods, which I have used in India for 

 the rough determination of the character of soils, may prove useful : — 



