28 THE ELEMENTS OF PLANT FOOD 



difference between the soft, or winter, wheats and the hard, or spring, 

 wheats is due to the varying proportion of these substances in the 

 gluten. A larger proportion of gliadin makes a soft wheat. 



Alkaloids make up another class of nitrogenous 

 compounds that are sometimes called the active prin- 

 ciples of plants because of their active effects when 

 taken into the body. Many of the alkaloids are used 

 in medicine and most of them are poisonous. The 

 following are some of the most common alkaloids : 



From Peruvian bark Quinine 



From tobacco Nicotine 



From coca leaves Cocaine 



From white poppy pods Morphine 



From black pepper Piperine 



From nux vomica Strychnine 



^ CARBON (C) 



Description and Occurrence. The elements hereto- 

 fore considered in their uncombined state are in the 

 form of gases. Carbon, however, as found free in na- 

 ture is a solid. In its free or natural state it may exist 

 as a diamond, which is a crystalline form of carbon, 

 and graphite, which is found in the crystalline and non- 

 crystalline forms. 



When combined with oxygen it forms carbon dioxide, 

 CO;>, a constituent of the air on which all vegetable 

 life feeds. All vegetable and animal bodies contain C, 

 and when these bodies are heated with an insufficient 

 supply of O another form of non-crystalline carbon is 

 formed ; namely, charcoal. Combined with H, and 

 also free, carbon occurs in coal, petroleum, and the 

 many forms and products of these substances. United 



