THE SOIL 323 



compare the two. The material left after washing consists 

 of stones, grit, and sand. 



Or put a little soil into a tube, add water, and shake. 

 Allow it to settle and note how the layers arrange them- 

 selves. The coarsest are at the bottom, succeeded by 

 layers of finer and finer materials, the water above holding 

 the finest particles for days in suspension, while floating on 

 the surface will be numerous fragments of decaying leaves 

 and stems. The part which settles slowly from the muddy 

 water is very fine and sticky like clay, but dark-coloured 

 with the organic matter. Spread a layer of this on a tin lid 

 and bake it : see what happens. It shrinks and cracks just 

 as clayey ground does in hot dry weather. Now add water 

 to it. Does it regain its original properties ? Baking has 

 destroyed its adhesiveness. 



Take three glass slips, place on each a drop of water, then 

 a little sand, loam, and clay respectively, and cover with 

 cover-glasses. Examine them under the microscope and 

 note the sizes, forms, and appearances of the particles. 

 Examine humus and peat in the same way, and look for 

 fragments of tissues, e. g. fibres and vessels. Can you find 

 any threads of mould on the decaying parts of plants ? 



Dark garden-soil consists of small stones, grit, sand, clay, 

 organic matter, and water. It differs strikingly from sub- 

 soil in containing much organic matter, and when this is 

 present plants grow well in it. It seems likely, therefore, 

 that from this plants get much of their food. 



But before the organic matter is of use it has to be de- 

 composed and converted into soluble inorganic salts, as 

 plants can only take up their food-materials in solution. 

 Hence a fertile soil must contain organic matter, must have 

 the means of decomposing it, and must possess a suitable 

 water-supply to dissolve the salts when formed. 



Organisms in the soil and their work. What are the agents 

 in the soil which act upon the organic matter ? Can we 



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