THE LOCUSTS 177 



Last, but not least, among their merits stands the fact 

 that leguminous plants are the only ones that actually en- 

 rich the soil they grow in, whereas the rest of the plant 

 creation feed upon the soil, and so rob it of its plant food 

 and leave it poorer than before. 



Pod-bearers have the power to take the nitrogen out of 

 the air, and store it in their roots and stems. The decay of 

 these parts restores to the soil the particular plant food 

 that is most commonly lacking and most costly to replace. 

 Farmers know that after wheat and corn have robbed the 

 soil of nitrogen, a crop of clover or cow peas, plowed 

 under when green and luxuriant, is the best restorer of 

 fertility. It enriches by adding valuable chemical ele- 

 ments, and also improves the texture of the soil, increasing 

 its moisture-holding properties, which commercial ferti- 

 lizers do not. 



Seventeen genera of leguminous plants have tree repre- 

 sentatives within the United States. These include about 

 thirty species. Valuable timber trees are in this group. 

 All but one, the yellow-wood, have compound leaves, of 

 many leaflets, often fernlike in their delicacy of structure, 

 and intricacy of pattern. With few exceptions the flowers 

 are pretty and fragrant in showy clusters. The ripening 

 pods of many species add a striking, decorative quality to 

 the tree from midsummer on through the season. Thorns 

 give distinction and usefulness to certain of these trees, 

 making them available for ornamental hedges. 



THE LOCUSTS 



Three representatives of the genus robinia are among our 

 native forest trees. They are known in early summer by 



