185 



and short stubble. The roots and stubble alone of hairy vetch 

 contained about four-fifths as much nitrogen as the entire rye 

 plant. 



Both heavy and light applications of non-nitrogenous 

 fertilizers were profitably applied to hairy vetch. 



Soil Improving Plants and Root Tubercles. 



In several experiments described in Bulletin No. 95 of 

 this station the land was left in a much more fertile condition 

 by plowing under a crop of cowpea vines than by turning 

 under a growth of crabgrass and weeds. The cowpeas had 

 stored up fertility, the other plants had not. 



Examination of the roots of the plants shows that cowpea 

 roots have many roundish enlargements, while roots of crab 

 grass, most weeds, cotton, corn, etc., are free from swellings 

 of this character. 



The name tubercle or nodule is applied to these enlarge- 

 ments, which maybe found on all thrifty cowpea plants, clover 

 plants, etc. If these tubercles are present the plant bearing 

 them is a renovating or soil-improving plant. All plants on 

 which these nodules can grow belong to the class of 

 leguminous plants or legumes. 



Leguminous plants, unlike others, are able to obtain 

 from the air a large proportion of the nitrogen required for 

 growth. This power to collect or " fix " atmospheric nitrogen 

 resides, not in the flowering plant itself, but in the tubercles 

 attached to its roots. 



Each of these enlargements, nodules, or tubercles, is filled 

 with myriads of miscroscopic germs or bacteria, which feed 

 on the gaseous nitrogen found in limitless amounts in the 

 atmosphere. Air, and consequently free or gaseous nitrogen, 

 circulates in all cultivated soils and comes in contact with 

 root tubercles. The germs within these nodules seize this 

 nitrogen, which flowering plants cannot directly utilize, and 

 change it into a form suitable for nourishing these higher 

 plants. The nitrogenous food thus prepared in the tubercle 



