48 Practical Farming 



with similar grain. This sand was kept moist with water 

 that was leached through a fertile soil similar to that in 

 the first-named pots, thus getting as much as possible of 

 the soluble plant food in the soil. Another pot of the 

 sand was watered with distilled water. This last pot pro- 

 duced plants to the extent only of the plant food in the 

 seed sown and then died. The pots watered with the soil 

 leachings grew feebly and finally died, showing that the soil 

 leachings alone did not furnish food enough for the plants. 

 These experiments seem to confirm the opinion that the 

 roots of the plants themselves have a solvent power on 

 matter in the soil which is not directly soluble in the soil 

 water. It also goes far to explain the fact that matter, 

 like pulverized phosphatic rock, which the chemist decides 

 is insoluble in water, when placed in the soil, does feed 

 the crop. While, therefore, the presence of water is essen- 

 tial in the soil, the solution of plant food is not altogether 

 dependent on the water, and experiments made to show 

 that the water-soluble food in all soils is very similar are 

 misleading, since they take no account of the work of the 

 plant roots themselves, which not only take part in the 

 solution but, as we shall see later, have the power to select 

 the foods they particularly need in different percentages 

 in different crops. 



Effects of Movements of water in the soil are often 



Atmospheric due to the soil air and its expansion and con- 

 Pressure on traction. Springs and small streams will 

 Supply^^ often swell up for the same reason that the 



mercury falls in the barometer, that is be- 

 cause of lessened air pressure. Changes in the barom- 

 eter are very commonly accompanied by changes in the 



