350 CHEMISTRY. 



CHAPTER XXVIII. 



SOILS AND MANURES. 



486. Soil the Food of Plants. There is a striking analogy 

 between the root of a plant and the stomach of an animal. 

 In both there are minute absorbents which take up the 

 material for growth. As the food put into the stomach is 

 not all nutritious, and the absorbents take from it that 

 which is so, so also the soil, the food of plants, as it is min- 

 gled with the fine branches of the roots, has its nutritious 

 portion absorbed by the little mouths which are there ever 

 open to receive it. The root, therefore, may be regarded 

 as the stomach of the plant. The proportion of nutritious 

 substance is much greater in the food of the animal than in 

 that of the plant, and therefore the stomach of the latter is 

 a much more extensive organ than that of the animal. 



487. Loosening the Soil. As food put into the stomach 

 of an animal more readily furnishes its nutritious part to 

 the absorbents if it be well masticated, so it is with the 

 food of the plant. Hence the necessity of preparing the 

 ground for plants by plowing, digging, etc. ; and hence y 

 also, the usefulness of loosening the ground about plants 

 so well known to the gardener. One of the evils of an 

 abundance of clay in a soil is the close, compact character 

 which the clay gives to it. The cold of winter has much 

 influence in preparing the soil for the coming growth of 

 spring, for, as the ground freezes, the expansion of the wa- 

 ter, which is mingled up with its particles as it changes 

 into ice, separates these particles from each other, and thus 



