262 CAUSES OF FERTILITY AND STERILITY [chap. 



the carbonate of lime, has already been discussed. 

 The soil becomes much less retentive of water, perco- 

 lation is increased so that the limed land is drier 

 and warmer, admits of cultivation at an earlier date 

 in the spring, and is far more friable when dry. 

 In fact, the liming gives a coarser texture to the clay 

 soil, and all the effects pertaining to the coarser texture, 

 such as diminished capacity for retaining water and 

 consequent greater warmth, less shrinkage and tendency 

 to cake on drying, are all manifest after the application 

 of lime. It does not, however, follow that the crop 

 will mature more readily though the season is made 

 earlier through liming ; in many cases in dry seasons 

 crops upon clay ripen prematurely, because the drying 

 up and shrinkage of the impervious clay cut the 

 roots off from all access of moisture. The liming, 

 by opening up the soil to the motion of water by 

 surface tension, keeps the plant growing for a longer 

 period ; at the same time, the increased amount of plant 

 food rendered available also tends to prolong the dura- 

 tion of growth. On very light soils the addition of lime 

 acts to a certain extent as a binding material, and in- 

 creases the cohesion and water-retaining power of the 

 soil, but it is not so effective in this respect as humus. 

 Besides its physical effect upon the texture of stiff soils, 

 lime has a very powerful chemical effect, liberating freely 

 the reserves of plant food of all kinds in the soil and 

 rendering them available to the plant ; so that on soils 

 naturally deficient in carbonate of lime, manures of all 

 kinds can only find their proper value if lime be also 

 used from time to time. On soils that have been 

 under intensive cultivation for a long time immense 

 reserves of plant food have been accumulated, which 

 only require the addition of lime to bring them into 

 action. As an example may be quoted the result of 



