32 Subtropical Vegetable-Gardening 



air indirectly. Plants that do not appropriate it from the 

 air are still important conservators of nitrogen, in that 

 they take it up from the soil and keep it from wasting, and 

 at the end of their life give it back when they decay. This 

 class of plants cannot give to the soil more nitrogen than 

 they draw out, but they can conserve it for subsequent 

 crops. They also accumulate the other soluble elements 

 of plant-food. The nitrogen-assimilating plants store 

 up varying amounts of this element and give it to the soil 

 when they decay, thus actually adding to the supply of 

 this important element, and also keeping the other ele- 

 ments from wasting. By growing a leguminous cover- 

 crop on land for a number of years, and utilizing it care- 

 fully, the land becomes richer, until finally it will grow 

 full crops. 



The best plants for gathering nitrogen now in cultiva- 

 tion in the southern United States are velvet beans, cow- 

 peas, and beggarweed. In tropical countries, green gram 

 or woolly pyrol, jack bean, Manila bean, Bengal bean, 

 pigeon pea, and several other legumes are used. Most 

 varieties of cowpeas are severely attacked by the root- 

 knot-producing nematode. This should be taken into 

 consideration when planting them, as it would mean the 

 failure of a subsequent non-immune crop if the field were 

 infested with these nematodes. Fortunately there is at 

 least one variety of cowpea, the Iron, that seems to be 

 resistant to this disease. 



As to the way of using these plants, there is some diver- 

 sity of opinion. In clay soil, the plants may be plowed 

 under in the green state, but on sandy soils this will not 

 be found good practice. 



