118 THE PRACTICAL SIDE OF 



height of two to three inches lucerne was 

 drilled across it and rolled in. The seed 

 germinated well, but when the young plants 

 had reached a height of some two inches they 

 died off, except upon the land which was 

 dunged. Here they continued to grow with 

 great luxuriance, until at harvest they had 

 reached a height of fourteen inches. The 

 failure on the land which received the slag 

 was not occasioned by vv^ant of food, for it 

 was well supplied with two materials in 

 which it was originally deficient — phosphoric 

 acid and hme; the third material, nitrogen, 

 lucerne is able to obtain from the atmos- 

 phere when the soil contains the requi- 

 site bacteria. These organisms, however, 

 were absent, as shown by the result, and, 

 being consequently unable to obtain free 

 nitrogen, the plant died off and the crop 

 v/as lost. On the other hand, the roots of 

 the lucerne growing in the land which was 

 dunged was well furnished with nodules, 

 and the plants were consequently enabled to 

 obtain free nitrogen in addition to the combined 

 nitrogen in the dung. The value of dung, 

 therefore, consists not only in the fact that 

 it provides plant food, but that it supplies 

 the soil with bacteria. For this reason the 



