104 ELEMENTS OF FARM PRACTICE 



The roots of the alsike clover extend into the soil to consider- 

 able depth, however, thus enabling the plants to draw on 

 the subsoil to some extent for plant food. This clover also 

 adds a large amount of vegetable matter to the soil by its 

 roots. Both alsike and medium red are very beneficial to 

 heavy soils, by opening them and letting in air when the 

 roots decay. They are beneficial to sandy soils by adding 

 large amounts of vegetable matter, thus making the soils 

 capable of holding more moisture. 



White clover roots are very small and fibrous. No 

 taproots are found, and the fibrous roots do not go nearly 

 so deep as the roots of the other clovers. The plants grow 

 so thickly, owing to their habit of spreading, that they 

 thoroughly cover the ground and keep the surface soil well 

 supplied with vegetable matter. 



Clover Adds Nitrogen to the Soil. — Clover possesses, 

 beside its heavy root system, another feature which makes 

 it a valuable crop to improve the soil. If a clover plant is 

 carefully dug from the soil, small bunches or nodules about 

 the size of an ordinary pin head will be seen on the roots. 

 See Figure 45. These are caused by bacteria. Bacteria 

 are a very low form of plant life. They are unable to live 

 from the soil as higher plants do, but must depend upon 

 plant or animal substances to supply them with organic 

 matter. Disease germs, the germs that cause milk to sour, 

 the germs that cause decomposition or rotting, etc., are 

 also bacteria. Some bacteria live on dead matter, others 

 on live matter. The latter are called parasites. The 

 bacteria causing the nodules on clover roots are in a sense 

 parasites, but in this case they are beneficial; they do some- 

 thing for the clover plant that it is unable to do for itself. 

 All plants require a large amount of nitrogen for food. A 

 very large proportion of the air is free nitrogen. Our com- 

 mon field crops are unable to make use of this nitrogen; 

 but clover, alfalfa, peas, beans and other plants belonging 

 to the family called legumes have the habit, which no other 

 class of plants has, of forming a sort of partnership rela- 

 tion with these bacteria and through them are enabled to 

 draw upon the nitrogen of the air. These nitrogen-gather- 

 ing bacteria have the power to absorb the nitrogen from 



