CLOVER. 



Another great source of single plant food — nitrogen — is the clover 

 plant and its relatives, such as the cow pea and the vetches. But does 

 not clover get its food from the soil like other plants? It gets miich 

 of its food from the soil, but it has the highly useful faculty of get- 

 ting the most expensive plant food — nitrogen — from the air. How 

 does this plant do what other plants can not do? If you will dig up 

 a healthy growing clover plant and carefully wash the earth from its 

 roots yo"u will find a number of thickened places on the smaller roots. 

 These look as though the roots might have been stung by some insect. 

 AVithin these enlarged places on the roots are many very minute or- 

 ganisms too small to be seen by the naked eye, yet these minute be- 

 ings are of great importance in the world. They have the power of 

 taking up the free uHrogcn of the air and converting it into a form 

 which the clover plant can use for food. These little organisms live 

 only on the roots of the clovers and related plants. So these plants 

 can serve as a means of gathering the most expensive of plant foods 

 and fixing it in a form suitable for food for plants or animals. The 

 use of clover for this purpose is one of the forms of green manuring. 

 Yet the clover brings but one element to the soil, and while it is of im- 

 mense value, it is not to be forgotten that plants require other things 

 for food, and we must not allow these other things to be continually 

 removed from the soil without making a suitable return. 



COMMERCIAL FERTILIZERS. " 



When the home supply of plant food has been utilized it may be 

 that still more can be very profitably used. Since material from 

 outside sources must be transported considerable distances, it generally 

 takes the form of concentrated manures called commercial fertilizers. 



Farmyard manures are all of the same general type, but commercial 

 fertilizers differ very widely among themselves, and may contain 

 one, two or three of the most important plant foods. These foods 

 may be in various forms, some of which are more quickly avail- 

 able to plants than others. One of the earliest and best forms 

 of wheat fertilizers was finely grottnd bone. On this account a 

 custom has grown up of calling all fertilizers "bone dust," no matter 

 what they may contain. Yet a mowing machine and a self-binder 

 may be less different from each other than are two fertilizers sold 

 under this common term. 



