158 ACTIOX OF SOIL ON FOOD OF PLANTS IN MANURE. 



finding out one that might serve to restore the original 

 j^roductive power of the field, and such a manure they 

 have not found. 



Messrs. Lawes and Gilbert assume that, with respect to 

 the soil, the clover plant bears the same relation as wheat 

 or barley; and finding that on a field (wliereon, notwith- 

 standing the richest manure, clover had failed) an abun- 

 dant barley or wheat crop was obtained the year after, it 

 became a settled conviction with them that tlie fixilure of the 

 clover had been caused by a specific disease generated in 

 the soil by the cidtivation of clover ; this disease would 

 attack the clover plant, but not the roots of wheat or 

 barley. 



Clover differs entirely from the cereal plants in tliis 

 respect, that it sends its main roots perpendicularly down- 

 wards, when no obstacles stand in tJie way, to a 

 depth which tlie fine fibrous roots of wheat and barley 

 fail to reach; the principal roots of clover (as may be 

 seen more especially with Trifolium pratense) branch off 

 into creeping shoots, which again send forth fresh roots 

 downwards. 



Thus clover, hke the pea plant, derives its principal food 

 from the layers beloAv the arable surface soil ; and the 

 difference between the two consists mainly in tliis — that 

 the clover, from its larger and more extensive root-sur- 

 face, can still find a sufiiciency of food in fields where 

 peas will no longer thrive : the natural consequence is, 

 that the subsoil is left proportionably much poorer by 

 clover than by the pea. 



Clover-seed, on account of its small size, can furnish 

 from its own mass but few formative elements for the 

 young plant, and requires a rich arable surface for its 

 developement ; but the plant takes comparatively little 

 food from the surface soil. When the roots have pierced 



