EFFECT OF XITROGKNOUS FOOD. 331 



is the great iiieqiuility in the appccarance of tlie young 

 crops, when sucli manures are apphed in comparative 

 experiments. The cereal plants upon fields manured 

 with guano or nitrate of soda are distinguislied before 

 others by a deep green colour, and by broader and more 

 numerous leaves ; but the harvest is generally far from 

 corresponding to the expectations raised by this promis- 

 ing appearance. Upon a iicld excessively rich in nitro- 

 genous food, there is a kind of rankness in the early 

 growth like that produced by a hot-bed : the leaves and 

 stalks are wateiy and weak, in consequence of the Avant 

 of time in their over-hasty growth to absorb contempo- 

 raneously from the soil the necessary quantity of sub- 

 stances, such as sihcic acid and lime, capable of commu- 

 nicating to their organs a certain solidity and power of 

 resistance against those external causes which endanger 

 their existence. The stalks fail to acquire the necessary 

 stiffness and strength, and are always hable to be laid, 

 especially upon lime soils. 



This injiu-ious mfluence of excess of nitrogenous food 

 is particularly remarkable in the case of the potato plant ; 

 for if it groAvs upon a soil excessively rich in nitrogenous 

 food, and the temperature should suddenly fall and wet 

 weather supervene, the plant is often attacked by the so- 

 called potato disease ; wliile a neighbouring potato field 

 merely manured with ashes shows no trace of it. 



Among all the many experiments which have been 

 liitherto made by farmers to improve their land, there is 

 not one instituted for the purpose of ascertaining the 

 actual condition of their soil, or of seeking proofs for tlie 

 correctness of the notions which they had once adopted. 

 The reason of their indifference about obtaining proofs for 

 their views chiefly consists in this, that the practical man, 

 like the artisan, is guided in his business not by ideas. 



