192 ENRICHING THE SOIL. 



orate and improve the soil, rather than to exhaust it. 

 This apparent anomaly is explained by the fact that all 

 leguminous, broad-leaved plants derive a large propor- 

 tion of their nutritive materials from the atmosphere, 

 and that a vast quantity of roots are left to decay in 

 the soil when it is at last broken up, varying, of course, 

 with the length of time the plant continues in the soil, 

 while the luxuriant foliage serves to shade the soil, and 

 thus to increase its fertility. Much of this rich foliage 

 is scattered and left to decay, as is the case with all 

 similar plants at the time of harvesting, and the growth 

 of the aftermath is also usually very considerable. The 

 fact that it actually increases the fertility of the soil for 

 other plants has often been proved, and may be re- 

 garded as fully established. A soil which would bear 

 only a medium crop of wheat at first, produced a greatly 

 increased quantity after being laid down to lucerne a 

 few years, till its roots had enriched the soil. 



Lucerne should not follow immediately after having 

 been grown a few years on the same soil, and then 

 broken up ; but after the land on which it has been 

 grown has been cultivated with some other crop, or 

 laid down to the natural grasses a length of time equal 

 to that during which it had previously remained in 

 lucerne, it can safely be sown again with it. 



The seed of lucerne, when fresh and good, is yellow, 

 glossy, and heavy. If the seeds are white, it is an indi- 

 cation that they are not ripe. If they are brown, we 

 may infer that they have been subjected to too strong 

 a heat to separate them from their husks. In either of 

 these cases, it is not safe to purchase or to rely upon 

 them. The same may be said of clover, and it is desir- 

 able to try them by a simple method, which will be indi- 

 cated hereafter in speaking of the selection of seed. 

 As the seeds of lucerne are somewhat larger than 



