BACTERIA AND PLANT FOOD 281 



now offers to the public small culture tubes of the microbes 

 of each of the important leguminous crops, with precise 

 directions for their use. This enables any one to inoculate 

 his soil for any crop desired. 



Experience has shown that with some crops at least it is 

 worth while at first to grow the same crop for two suc- 

 cessive seasons in order to secure a thorough inoculation of 

 the soil. After that, if the crop is grown in rotation every 

 four or five years, the microbes are likely to continue 

 present in such numbers that further inoculation is un- 

 necessary. 



The germs that grow upon cowpeas seem very generally 

 present in the soil of the Southern states. Consequently 

 it is seldom necessary to inoculate for this crop. 



The germs that grow upon sweet clover or melilot seem 

 to be able to develop with equal vigor upon alfalfa. Con- 

 sequently, it is often practicable to inoculate alfalfa fields 

 with soil in which sweet clover has been growing. 



OBSERVATIONS FOR PUPILS 



1. Make a list of the leguminous plants in your locality upon which 

 you find root tubercles. 



2. Compare the abundance of the tubercles with the vigor of the 

 plant. 



3. Grow red clover in sand or other soil deficient in nitrogen, being 

 sure it is from a field where red clover has not grown. Apply the 

 germs obtained as suggested on page 280, to part of the pots, but not to 

 all. See which set grows best, making sketches every two weeks. 



4. Read such of these references as your teacher directs : 



Leguminous Crops for Green Manuring, Farmers' Bulletin 278. Progress in 

 Legume Inoculation, Farmers' Bulletin 315. The Renovation of Worn-out Soils, 

 Farmers' Bulletin 245. Alfalfa, Farmers' Bulletin 339. Clover Farming on the 

 Sandy Jack-pine Lands of the North, Farmers' Bulletin 323. Canadian Field 

 Peas, Farmers' Bulletin 224. Cowpeas, Farmers' Bulletin 318. The Liming of 

 Soils, Farmers' Bulletin 77. 



