THE PROPERTIES OF SOIL 27 



chances of a spell of corrective frost are 

 past ; mistakes in autumn are of less account, 

 and the less so the more severe the winter 

 that follows. In the case of clay, as in the 

 case of sand, the addition of humus does 

 much to improve its character in the way of 

 cohesiveness ; for whereas this substance 

 increases the cohesiveness of sand it has the 

 opposite effect on clay, making it more 

 easily broken down and brought into a 

 desirable mechanical condition. 



Then, again, not only must the particles 

 of soil possess the property, within limits, 

 of sticking together, but they must also have 

 the power of retaining water. Soil may be 

 practically sterile either because it contains 

 too little water or because it contains too 

 much, the proper degree of moisture as a rule 

 being reached when the soil feels damp to 

 the hand. It is on the water that is held 

 between the soil particles that plants feed, 

 and through which agency they derive all the 

 mineral material which is vital to their 

 existence. In the case of sand, the capacity 

 of the soil to retain water is increased by the 

 addition of humus, whose power of absorbing 

 water is much greater than that of sand itself. 

 Clay also is improved by the addition of 

 humus, which, to some extent, loosens the 



