138 



ROTATION OF CROPS. 



formed without the existence of analogous intermediate members 

 of the series. 



Now, if the organic compounds rich in oxygen, viz. the acids, 

 be the means of producing the compounds poorer in this element, 

 such as sugar, starch,- &c, then the alkalies and alkaline bases 

 must be looked upon as the conditions essential for the formation 

 of these non-azotized constituents, because the acids existing in 

 cultivated plants are generally in the form of salts and are rarely 

 free. An organic acid may perhaps be formed without the pre- 

 sence of these bases, but, in the absence of an alkali, or of a body 

 possessing an analogous action, sugar, starch, gum, and pectin, 

 cannot be formed in the organism of a plant. Sugar is not formed 

 in those fruits and seeds in which the organic acids are free, that 

 is, in which they do not exist as salts, as, for instance, citric acid 

 in the lemon, or oxalic acid in the chick-pea. It is only in plants' 

 containing the acids combined with bases in the form of soluble 

 salts, that sugar, gum, and starch, are produced. 



It is a matter of little consequence what value is attached to 

 the opinion now given of the part taken by alkaline bases in the 

 process of vegetable life. But the following facts are of the great- 

 est significance and value to agriculture, namely, that the newly- 

 developed sprouts, leaves, and buds,* or in other words, those 

 parts of the plants possessing the greatest intensity of assimilation, 

 contain the greatest proportion of alkaline bases, and that the 



* 1000 parts of Firwood gave 3 "28 parts of ashes. 

 1000 " Fir-leaves " 62 "25 " 



The ashes of the leaves of the fir amount to more than 20 times those in 

 the wood freed from its bark 100 parts of the former contain :— (Hert- 

 wig) 



- 1072 



Alkaline carbonates > 

 Common salt - - > 

 Sulphate of Potash 

 Silicate of Potash 

 Carbonate of lime - 



'• magnesia - 



Phosphate of magnesia > 



" lime > 



Basic perphosphate of iron 

 Basic phosphate of alumina 

 Silica 



12*79 salts soluble in water. 



8630 compound b insoluble in water 



