268 ON THE SUCCESSION OF CROPS. 



There are some plants, which, though generally 

 raised for the sake of their seed, exhaust the soil less 

 than the grains : these are of the numerous family of 

 leguminous plants, and which sustain a middle rank 

 between the two of which I have just spoken. Their 

 perpendicular roots divide the soil, and their large 

 leaves, and thick, loose, porous stalks readily absorb 

 air and water. These parts preserve for a long time 

 the juices with which they are impregnated, and yield 

 them to the soil, if the plant be buried in it before 

 arriving at maturity : when this is done, the field is 

 still capable of receiving and nourishing a good crop of 

 corn. Beans produce this effect in a remarkable de- 

 gree ; peas to a less extent. 



Generally speaking, those plants that are cut green, 

 or whilst in flower, exhaust the soil but little: till this 

 period they have derived their support almost exclu- 

 sively from the air, eaith, and water; their stalks and 

 roots are charged with juices, and those parts that are 

 left in the earth after mowing will restore to it all that 

 had been received from it by the plant. 



From the time when the seed begins to be formed, 

 the whole system of nourishment is changed: the plant 

 continues to receive nourishment, for the perfecting of 

 its seed, from the atmosphere and the earth, and also 

 yields to the grain all the juices it had secreted in its 

 own stalks and roots: by this means the stalks and 

 roots are dried and exhausted. When the fruits have 

 arrived at maturity, the skeleton remains of the plant, 

 if abandoned to the earth, restore to it only a small 

 portion of what had been taken from it. 



The oleaginous seeds exhaust the soil more than the 

 farinaceous seeds; and the agriculturist cannot be at 

 too much pains to free his grounds from weeds of that 

 nature, which so readily impoverish them ; especially 

 from the wild mustard, sinapis arvensis, with which 

 cultivated fields are so often covered. 



