ROTATION OF CROPS. 27T 



" This classification, however, is obviously only a very general 

 " one, and permits division into a great number of subordinate 

 " classes ; particularly with respect to those plants in which the 

 " alkalies may be replaced by lime and magnesia. * * * 



" The potato plant belongs to the lime plants as far as regards 

 " the ingredients of its leaves, but its tubers (which contain only 

 " traces of lime) belong to the class o^ potash plants. With refer- 

 " ence to the siliceous plants, this difi^erence of their parts is very 

 " marked. 



" Barley must be viewed as a lime plant, when compared with 

 " oats or with wheat, in reference to their ingredients soluble in 

 " muriatic acid ; but it would be considered as a siliceous plant, if 

 '' viewed only in reference to its amount of silica. Beet-root 

 " contains phosphate of magnesia, and only traces of lime, while 

 " the turnip contains phosphate of lime and only traces of mag- 

 '' nesia. 



" When we take into consideration the quantity of ashes, and 

 *' their known composition, we are enabled to calculate with ease, 

 " not only the particular ingredients removed from a soil, but also 

 " the degree in which it is exhausted of these by certain species of 

 " plants belonging to the potash^ lime^ or siliceous plants. This will 

 " be rendered obvious by the following examples : — 



"A soil, consisting of four Hessian acres, has removed from it by a crop of — 

 Salts of potash Salts of" lime, magnesia, 



and soda. and peroxide of iron. Silica, 



lbs. lbs. lbs. lbs. lbs. 



Wheat./;" ""'^ 95-31 \o-5i 3475 | 67-55 ^6005 



( In corn 35-20 J •* ^ 32-80 J ■'-' -* 



o f In straw 150-4.0) ^ 54-80 ) , 



Peas, ■< T ^ }■ 104-41 ^J; ,„ J- -!7i-46 4660 



(.In corn 44'02 j ^* ^ 16-68 J ^' ^ ^ 



„.,_ ( In straw 40-73 ) o o 3600 / „ 



^y^- 1 In corn 4^-05! ^^-7^ L-Szf 57-8z 13977 



Beet-root without leaves 361-00 37'8'}- 



Helianthus tuberosus 55600 104-00 



"The same surface is deprived by these crops of the following quantity of phos- 

 " phates : — 



Helianthus 

 Peas. Wheat. Rye. tuberosus. Turnips. 



117 II--43 7705 1^2 3784 



