The Effect of Climate and Weather on the Soil. 5 
and dying off when it is exhausted. It is this that constitutes 
the vital distinction between a heap of mineral matter and a 
soil. There is no soil without life and no life is possible 
without stored up energy. We are only beginning to know 
what this soil life is, but already some hundreds of different 
kinds of creature have been found. Some few are large 
enough to be seen. Of these the most important are the earth- 
worms, which burrow in the soil and effect a fine natural 
cultivation, letting in air and drawing in leaves, stems, and 
other vegetable debris from the surface to mingle with the 
mass of soil below. Most of the soil organisms are microscopic 
in size ; some are leading an active life, others are in the 
inert resting stage and are called spores or cysts. The very 
incomplete census taken so far shows that the numbers of 
micro-organisms living in a single salt-spoon full of soil must 
be reckoned in millions. 
The second effect of this addition of organic matter is also 
great ; the decay of the vegetation profoundly influences the 
amount of plant food in the soil. The first vegetation that 
sprang up must obviously have got its food — its calcium and 
potassium salts, phosphates, &c. — from the mineral particles, 
but new sources of food appear for the plants that come after. 
The first crop slowly decayed under the influence of the soil 
organisms and in decaying it set free those substances that its 
roots had taken as food and returned them again to the soil. 
Hence subsequent plants have food from two sources : the 
potassium salts, &c., dissolved by the soil water from the soil 
particles ; and in addition a supply of the same substances 
drawn by previous generations from the soil during their life- 
time, but afterwards set free on the decay of the dead tissues. 
The plant food, in fact, keeps circulating between the soil and 
the plant, and the organic matter constitutes the medium by 
which the circulation takes place. 
In our climate, and in humid climates generally, the decay 
of the plant residues is not complete, at any rate during the 
course of a few seasons, and some of the products accumulate 
as dark brown or black substances conveniently known by one 
name, humus. These substances have certain physical pro- 
perties which they impart to the soil, and they enable the 
cultivator to get a really good tilth. 
The character of the soil is therefore very much affected by 
the nature of the organic matter present, and this is largely 
determined by the type of vegetation that grows there and the 
extent to which the decomposition has proceeded in the soil. 
Now both these are climatic effects. Under dry conditions the 
plants tend to be narrow leaved and tough — pine needles, 
broom, &c., will at once occur as instances — whilst under 
