The Science of the Soil 123 



upper crust very soon becomes dry and hot, and almost incapable of sup- 

 porting any plant life. 



In a loamy soil, however, which is a mixture of sand, clay, and 

 organic material, moisture arises neither too quickly nor too slowly. It is, 

 therefore, retained round the roots for a longer period. 



The ascent of moisture depends not only upon the nature of the soil, 

 but also upon the way in which it has been cultivated. We find even 

 in good garden soils that have been dug only 9 in. or 1 ft. deep, that 

 the moisture soon vanishes from this upper layer. The subsoil beneath 

 is probably too firmly compressed to allow the moisture to travel upwards 

 freely. The same thing is seen in soils that have been ploughed year 

 after year. The upper layer of 6 in. or 9 in. rests upon a very hard 

 " pan ", through which water can neither penetrate downwards nor rise 

 upwards. 



If, however, we take a soil that has been broken up to a good depth, 

 say 2 and 3 ft., it will be noticed, even in the hottest and driest 

 summers, that there is always sufficient moisture available for the roots of 

 the plants growing on it, and they appear to be as fresh and green as if 

 they were supplied overhead with abundance of water each day. 



The way in which the water passes upwards from layer to layer and 

 particle to particle of the soil is known as capillary attraction. The 

 direction of the liquid is always from the wet to the dry, and the finer the 

 particles of soil, and consequently the narrower the interstices between 

 them, the greater the height to which the moisture will rise. 



This may be demonstrated by taking some glass tubes with bores of 

 various diameters. If placed on the surface of w^ater it will be noticed 

 that the liquid will rise higher and more quickly in the tube with the 

 smallest bore. 



It is possible also that the pressure of the atmosphere has something 

 to do with this ascent of liquid in the soil. The air spaces between the 

 particles may be regarded as so many fine-bored tubes, up which the water 

 passes. Owing, however, to the heat at the surface, the air and the mois- 

 ture become warmer and lighter, and rise upwards. A kind of vacuum is 

 thus caused, or at any rate both air and moisture are less dense than at 

 a lower depth. The equilibrium between top and bottom is thus upset, 

 and the water and air from beneath rush upward, owing to the pressure 

 of the atmosphere, to fill the vacuum caused, and to restore the balance. 

 During a hot day this process is going on vigorously, and moisture rises 

 to the surface in the same way that oil is drawn up the wick of a lamp 

 by the heat of the flame at the top. 



Every gardener who sows the spores of Ferns, or such fine seeds as 

 those of Gloxinias, Begonias, Rhododendrons, &c., takes advantage of the 

 capillarity of the soil, by dipping the seed pots in water, and allowing the 

 moisture to rise upwards to the surface instead of watering overhead. 



Conserving- the Moisture in Soil The Use of Hoeing- and Mulching-. 

 While the aim of the open-air cultivator should be to prepare his soil 



