82 SOURCE AND ASSIMILATION 



quantity of guano to a soil, which consists only of 

 sand and clay, in order to procure the richest crop 

 of maize. The soil itself does not contain the 

 smallest particle of organic matter, and the manure 

 employed is formed only of ur ate, phosphate, oxalate, 

 and carbonate of ammonia, together with a few 

 earthy salts. "* 



Ammonia, therefore, must have yielded the nitro- 

 gen to these plants. Gluten is obtained not only 

 from corn, but also from grapes -and other plants ; 

 but that extracted from the grapes is called vege- 

 table albumen, although it is identical in composi- 

 tion and properties with the ordinary gluten. 



It is ammonia which yields nitrogen to the vege- 

 table albumen, the principal constituent of plants ; 

 and it must be ammonia which forms the red and 

 blue colouring matters of flowers. Nitrogen is not 

 presented to wild plants in any other form capable 

 of assimilation. Ammonia, by its transformation, 

 furnishes nitric acid to the tobacco plant, sun- 

 flower, Chenopodium, and Borago qfficinalis, when 

 they grow in a soil completely free from nitre. 

 Nitrates are necessary constituents of these plants, 

 which thrive only when ammonia is present in 

 large quantity, and when they are also subject to 

 the influence of the direct rays of the sun, an influ- 

 ence necessary to effect the disengagement within 

 their stem and leaves of the oxygen, which shall 

 unite with the ammonia to form nitric acid. 



* Boussingault, Ann. de Ch. et de Phys. Ixv. p. 319. 



