150 ROTATION OF CROPS. 



Salts of Potash Salts of Lime 



and Soda. and Magnesia. Silica. 



Tobacco (Havannah) (1) - - 2434 67'44 830 



(Dutch) (4) - - -2307 62*23 1525 



« (grown in an arti- ) _ 5g . 00 

 ficialsoil(l) > 



Pea-straw (4) 27 82 63*74 7*81 



Potatoe-herb (5) 420 59*40 36 40 



Meadow-clover (1) - - - - 39 20 56-00 4*90 



Maize-straw (2) 71 00 6 50 18*00 



Turnips ------- 81*60 18*40 



Beetroot (6) 88 00 12*00 



Potatoes (tubers) (6) - - - 85*81 14" 19 



I Helianthus tuberosus (7) - - 84*30 15*70* 



Lime 

 Plants. *> 



Potash 

 Plants. 



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. As far as we 

 are authorized to judge by our present knowledge, a substitution 

 of soda for potash lakes place in our cultivated plants ; but it has 

 not yet been observed, that in these plants the alkalies can be 

 replaced by lime. 



The potatoe 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 of potash plants. With 

 reference to the siliceous plants this difference 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 con- 

 tains phosphate of magnesia, and only traces of lime ; while the 

 turnip contains phosphate of lime and only traces of magnesia. 



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 



In the above analysis, the figures 'represent the chemists as under:— 



(1) Wiegmann and Polstorf. (5) Berth i«r and Braconnot. 



(2) Saussure. (6) Hruschauer. 



(3) Fresenius. (7) Braconnct. 



(4) Hertwig. 



