150 HOW CROPS GROW. 



of the albuminoid principles) is not tmfrequently pres- 

 ent as a nitrate in the tissues of the plant. It usually 

 occurs there as potassium nitrate (niter, saltpeter), 

 KNOs. 



The properties of this salt scarcely need description. 

 It is a white, crystalline body, readily soluble in water, 

 and has a cooling, saline taste. When heated with car- 

 bonaceous matters, it yields oxygen to them, and a defla- 

 gration, or rapid and explosiTe combustion, results. 

 Touch-paper is paper soaked in solution of niter and 

 dried. The leaves of the sugar-beet, sunflower, tobacco, 

 and some other plants, frequently contain this salt, and, 

 when burned, the nitric acid is decomposed, often with 

 slight deflagration, or glowing like touch-paper, and the 

 alkali remains in the ash as carbonate. The characters 

 of nitric acid and the nitrates are noticed at length in 

 " How Crops Feed." 'See also p 



Oxalates, Citrates, Malates, Tartrates, and salts 

 of other less common organic acids, axe generally to be 

 found in the tissues of living plants. On burning, the 

 metals with which they were in combination — potassium 

 and calcium, in most cases — remain as carbonates. 



Ammonium Salts exist in minute amount in some 

 plants. What particular salts thus occur is uncertain, 

 and specialnotice of them is unnecessary in this chapter. 



Since it is possible for each of the acids above described 

 ' unite with each of the bases in one or several propor- 

 tions, and since we have as many oxides and chlorides as 

 there are metals, and even more, the question at once 

 arises — which of the 60 or more compounds that may thus 

 be formed outside the plant do actually exist within it ? 

 In answer, we must remark that while most or all of them 

 may exist in the plant but few have been proved to exist 

 as such in the vegetable organism. As to the state in 

 jvhich iron and manganese occur, we know little or noth- 

 ing, and we cannot always assert positively that in a given 



t 



