182 ON ROTATION OF CROPS. 



a second crop of grain the fourth year, which completes 

 the assolement. 



The rotation of crops must, however, necessarily vary 

 with the soil : that which I have described, from M. De 

 Candolle, is probably best adapted to France ; in England 

 turnips, I believe, are usually followed by barley, clover, 

 and wheat. 



Caroline. Pray, why should not trees require an as- 

 solement as well as corn and leguminous plants ? for the 

 exudations of a tree during the number of years it lives 

 must greatly injure the soil for another of the same kind. 

 Nay, I wonder how the same individual tree can thrive 

 throughout a long life in a soil so deteriorated. 



Mrs. B. You must consider, in the first place, that 

 the roots of a young tree are of small extent, and both 

 seek their food and give out their exudations in the ground 

 immediately surrounding the stem. In proportion as they 

 lengthen they extend their researches, spreading wider 

 and piercing deeper into the soil ; thus, after having ex- 

 hausted it of nourishment, and deteriorated it near the stem, 

 they find fresh aliment in a more enlarged sphere. 



Emily. Then when a tree dies, if another of .the same 

 kind be planted in its place, the young roots will find the 

 soil near the stem exhausted of nutritive particles, and 

 vitiated by exudations ? and yet, when a dead tree in an 

 avenue is replaced by another of the same species it grows 

 without difficulty. 



Mrs. B. If you replaced it by one of another family, 

 there is no doubt but that it would thrive better. One 

 of the same species is, however, not without resources ; 

 for you must consider that the soil nearest the stem of the 

 old dead tree has not been acted upon by the roots for a 

 number of years ; and, during this period of repose, it has 

 been able, in a great measure, both to renovate its nutri- 

 tive particles by the natural manure it receives annually 

 from the fall of the leaf, and to purify itself from exuda- 

 tions of the old tree, these being absorbed by the grasses, 

 underwood, and plants of various descriptions which sur- 



1000. How does assolement differ in England from what it is in 

 France! 1001. Why should not trees as well as corn and legumin- 

 ous plants require an assolement'? 1002. When a tree dies will 

 another of the same kind grow in the same place 1 ? 1003. Why did 

 not the soil suited to its nourishment be completely exhausted by supporting 

 the first 1 ? 



