138 Vegetable Physiology. 



8. That chlorous acid and ammonia can unite without decomposi- 

 tion, but that the compound which they form, is changed by water into 

 chlorine and azote. 



9. That the oxide of chlorine, obtained by the method of Stadion, 

 is composed of one volume of chlorine and two volumes of oxygen, 

 and is the same as that obtained by Davy. 



10. That the chlorous acid may become a constituent part of an 

 ether which is singularly disposed to a transformation into acetic 

 ether. — Annales de Chim. et dePhys. Oct. 1831. 



Art. XXII. — Vegetable Physiology in relation to Rotation of 



Crops ;^ by M. Macaire. 



Translated for this Journal by Prof. Griscom. 



In a memoir inserted in the transactions of the Societe de physique 

 et d''histoire naturelle of Geneva, this gentleman has developed some 

 physiological facts, interesting to science and to practical agriculture. 



A judicious rotation of crops is known to be a matter of great im- 

 portance. One kind of vegetable (A) will grow and flourish well in 

 a soil from which another kind of vegetable (B) has just been gath- 

 ered, while an attempt to raise another crop of the first vegetable (A), 

 or a crop of a third vegetable (C) immediately after the first (A) in 

 the same soil will be attended with little or no success. The discov- 

 ery of this fact which is almost as ancient as agriculture itself, is sup- 

 posed to have led to the practice of fallowing. A piece of fallow 

 ground will, almost to a certainty, be covered with a crop of weeds. 

 These being plants of a different nature, do not unfit the soil, but 

 prepare it for a succession of the same crop as that which preceded 

 them. But science or experience has taught the enlightened farmer, 

 to substitute useful plants in the room of weeds, and thus to keep his 

 grounds in profitable activity. 



Various reasonings have been employed to account for the neces- 

 sity of this rotation. 1st. That different plants absorb different juices 

 from the same soil, and that a piece of ground exhausted by culture, 

 may still be rich for another class of vegetables. But it is known 

 to physiologists, that plants absorb all the soluble substances that the 

 soil contains, whether injurious to their growth or not. 2d. That the 

 roots of different plants being of difl^erent lengths, extend into, differ- 

 ent layers of the soil, and thus derive from it appropriate nourishment. 



