176 ON ROTATION OF CROPS. 



vitiated for such plants by the long series of exudations 

 of their progenitors. 



Mrs. B. If Nature does not usually employ succes- 

 sive, she does simultaneous assolements. In her sponta- 

 neous forests she raises such a prodigious variety of trees 

 and shrubs, and in her meadows such a multiplicity of 

 herbs and grasses, that the different plants mutually sup- 

 ply each other with exudations. 



Emily. Besides, where Nature acts without restraint, 

 she enriches the soil not only by the annual fall of the 

 leaf, but, in the course of time, the whole plant, whether 

 grass, shrub, or tree, returns to the soil, to repay the 

 nourishment it had received during its -life. 



Mrs. B. The soil can never be impoverished by nat- 

 ural vegetation : that of forests, where man does not cut 

 down and carry away the trees, is not more exhausted of 

 nutriment at the present day than it was a thousand years 

 ago. 



Those magnificent forests which covered the face of 

 the greater part of America, when it was first known to 

 us, never had any other manure than the remains which 

 its vegetable and animal productions afforded ; nor can 

 a better be supplied. And we in some respects copy Na- 

 ture when we prepare the soil for corn by ploughing in, 

 a green crop of leguminous plants. 



There is nothing which exhausts either a plant or the 

 soil in which it grows, so much as the ripening of its 

 seeds. No animal labors with greater effort to support 

 its offspring than the poor plant to bring its seed to ma- 

 turity : it pumps up sap with all its powers of suction ; 

 yet, if it has much seed to ripen, after having accom- 

 plished its task, it frequently perishes through exhaustion 

 from the intensity of its efforts. 



Perennial plants have but few, and but small grains to 

 ripen, while those of annuals, are large and much more 

 abundant; and it is this difference, perhaps, which con- 

 stitutes the real distinction between these two classes of 

 plants : the one, exhausted by its efforts, dies after ripen- 



965. What does Mrs. B. say in reply of assolements 1 966. By 

 natural vegetation what effect is produced on the soiH 967. Of the 

 forests of America what is said? 968. What is most exhausting to 

 the plant and the soil! 969. What constitutes the principal difference 

 between perennial plants and annuals! 



