158 ACTION OF SOIL ON FOOD OF PLANTS IN MANURE. 



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 (whereon, 

 notwithstanding the richest manure, clover had failed) 

 an abundant barley or wheat crop was obtained the 

 year after, it became a settled conviction with them 

 that the failure of the clover had been caused by a spe- 

 cific disease generated in the soil by the cultivation 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 this 

 respect, that it sends its main roots perpendicularly 

 downwards, when no obstacles stand in the way, to a 

 depth which the fine fibrous roots of wheat and barley 

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

 seen more especially with TrifoUum pratense) branch 

 off into creeping shoots, which again send forth fresh 

 roots downwards. 



Thus clover, like the pea-plant, derives its principal 

 food from the layers below the arable surface soil ; 

 and the difference between the two consists mainly in 

 this that the clover, from its larger and more exten- 

 sive root-surface, can still find a sufficiency 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 through this, the upper parts are soon covered 

 with a corky coating, and only the fine root-fibres rami- 

 fying through the subsoil convey food to the plant. 



$Tow, if we look at the experiments made by Messrs. 

 Lawes and Gilbert to render a clover-sick field produc- 

 tive again for clover, we see, at once, that all the means 

 employed were well adapted to enrich the uppermost 

 layers of their field with nutritive substances for wheat 

 and barley ; but that the clover plant could derive ben- 



