276 APPENDIX TO PART I. 



of each, which the soil at any given time contains, may be 

 absorbed in an equal ratio. 



*'Thus a productive crop of corn could not be obtained, 

 without the phosphates of lime and magnesia which are 

 present in the grain, nor without the silicate of potass which 

 gives stability to the stalks. 



'*It would be injudicious, therefore, to sow any plant 

 that required much of any of the above ingredients, imme- 

 diately after having diminished the amount of them present 

 in the soil, by a crop of wheat, or of any other kind of corn. 



**But, on the other hand, leguminous plants, such as' 

 beans, are well calculated to succeed to crops of corn, be- 

 cause they contain no free alkalies, and less than one per 

 cent, of the phosphates. 



*' They thrive, therefore, even where these ingredients 

 have been withdrawn, and during their growth^ afford time 

 for the ground to obtain a fresh supply of them, by a fur- 

 ther disintegration of the subjacent rock. 



*' For the same reason, wheat and tobacco may some- 

 times be reared in succession in a soil rich in potass, be- 

 cause the latter plant requires none of those phosphoric 

 salts which are present in wheat. 



* ' In order, however, to proceed upon certain data, it would 

 be requisite, that an analysis of the plants most useful to 

 man should be accomplished in the different stages of their 

 growth, a labor which has hitherto been only partially un- 

 dertaken, and which perhaps is an object worthy to engage 

 the attention of a great Body, like that of the English Ag- 

 ricultural Association. 



** It is a curious fact, that the same plant differs in con- 

 stitution when grown in different cHmates. Thus in the 

 beet-root, nitre takes the place of sugar, when this plant is 

 cultivated in the warmer parts of France.* 



**The explanation of this difference is probably as fol- 

 lows : — 



''Beet-root contains, as an essential ingredient, not only 

 saccharine matter, but also nitrogen, and it is probable, 

 that the two are mutually so connected together in the veg- 

 etable tissue, that the one cannot exist without the other. 

 The nitrogen, being derived from the decomposition of am- 

 monia, must be affected by any cause which diminishes the 

 supply of the latter ; and in proportion as this ingredient 

 is wanting, the secretion of sugar will likewise fall off. 



''Now, it has been shown by Liebig, that the formation 



"* See Chaptal." 



