28o FARM FRIENDS AND FARM FOES 



to the seed and be planted with them to insure a good de- 

 velopment of tubercles upon the roots. 



Consequently, the conditions that exist in a given case 

 may be something like this : Here is a field in which no 

 red clover has been grown in a dozen years. The soil is 

 poor and sour. It produces very small crops and evi- 

 dently needs to be improved. We wish to grow red clover 

 to help its condition. Evidently we must get rid of the 

 sourness by a liberal application of lime or some other 

 alkaline fertilizer. Then we must introduce the clover 

 tubercle germs into the soil and sow the seed. Such intro- 

 duction of germs is often spoken of as inoculation — that 

 is, we inoculate the soil with the desired microbes in the 

 expectation that when introduced they will thrive and 

 multiply upon the clover roots. One of the simplest ways 

 of inoculating is to bring a quantity of soil from a field in 

 which clover has been growing successfully. Being sure 

 that the plants grown in the soil have shown plenty of 

 nodules, spread it broadcast and harrow it in. We may 

 thus get a very general dispersal of the germs where they 

 will come in contact with the developing clover roots. 



Another way to inoculate the soil is to shake up in a 

 bottle of water a small quantity of soil from a thriving 

 clover field. Let it stand until the soil particles settle, and 

 pour the clear liquid over the clover seed or upon the soil 

 where the seed is planted. This method is especially use- 

 ful in pot experiments. 



Fortunately, these nitrogen-gathering bacteria can be 

 induced to develop in vast numbers in what are called 

 nutrient solutions. The scientists of the United States 

 Department of Agriculture have been at work for many 

 years upon the methods of growing bacteria in such solu- 

 tions. They have succeeded so well that the Department 



