IMPORTANCE OF ALKALIES. 143 



Starch, sugar, and gum contain carbon and the elements of 

 water, but they are never combined with alkalies, nor do they 

 contain phosphates. We can suppose that two specimens of the 

 same plant, when supplied with the same amount of mineral food, 

 may yet form very unequal quantities of sugar and of starch ; 

 and that two equal surfaces of land prepared in exactly the same 

 manner may bear two samples of barley, the one of which may 

 yield half or double the weight of the seeds that the other does. 

 But the excess of weight must depend upon the amount of unni- 

 trogenous ingredients, and not on the constituents containing sul- 

 phur and nitrogen ; for if the same quantity of the inorganic 

 constituents of blood be supplied to the soil, and if they enter into 

 the plants, a corresponding quantity of the organic constituents 

 of blood must be formed in the seeds, so that one cannot contain 

 more than the other. A difference in the result can happen only 

 when the one plant receives a less supply of nitrogen than the 

 other, in a given time ; for when there is a deficiency of ammo- 

 nia, a corresponding quantity of the inorganic constituents of the 

 blood is left unemployed. 



When two species of plants are cultivated on a field of the 

 same nature throughout, that species which generates the greatest 



In the above analyses, the phosphates of the alkalies in the peas and 

 beans are contained and calculated as tribasic salts ; those in the seeds of 

 the cereals, as bibasic. The ashes of the seeds cannot effervesce with 

 acids, because they do not contain an alkaline carbonate ; in this respect 

 they are similar to the ashes of blood ; and it may be observed that the 

 salts in both are quite the same. If the ashes either of blood or of the 

 seeds be exposed to air, they absorb caroonic acid and moisture ; the tri- 

 basic phosphate becomes bibasic, and the third atom of alkali is converted 

 into a carbonate. 



