DESTRUCTIVE METABOLISM 415 



Alkaloids. — The alkaloids are numerous, and very important medi- 

 cinally, as they are dangerous poisons or useful local stimulants, according 

 to circumstances. A few, such as cajfein from tea and coffee, thcobromin 

 from the seeds of cacao ("cocoa "), and the deadly muscarin from the 

 poisonous mushroom {Amanita muscaria), are not related to the alka- 

 loids proper, which are for the most part derivatives of pyridin and chin- 

 olin. The true alkaloids are found in fungi and various seed plants, but 

 are* most common in certain families of dicotyls. For example, in the 

 Papaveraceae, the oriental poppy alone yields more than twenty alka- 

 loids, of which morphin, narcotin, and codein are best known ; in the 

 Solanaceae, tobacco contains 'nicotin and others, and most of the other 

 genera yield a tropin and a number allied to it; a great number of the 

 Apocynaceae have alkaloids in their latex, at least twenty different ones 

 being known; in the Rubiaceae, the cinchonas and their allies produce 

 more than thirty alkaloids, of which quinin and cinchonin are widely 

 known ; in the Loganiaceae, seeds of Strychnos nux-vomica yield strych- 

 nin and briicin, while another species yields several " curare " alkaloids ; 

 and in the Erythroxylaceae, coca yields among others cocain, at once 

 highly useful as a local anesthetic and utterly destructive to body and 

 mind when used habitually. 



Coloring matters of flowers, fruits, barks, seeds, etc., are too numerous and 

 varied to be discussed here. 



Ash. — Mineral salts are present, sometimes amorphous, incrusting 

 or incorporated in the cell walls, as is the case with silica; sometimes 

 crystallized, as is the case with calcium oxalate. The ash of plants 

 consists of the total mineral matter left as oxids when completely burned. 

 Analysis shows that the amount and content of the ash varies much in 

 the same plant in different situations, thus indicating that in part (and 

 doubtless in large part) these materials are determined not by the 

 " needs " of the plant but by the solutions which have opportunity to 

 wander into it. Cultures under special conditions have shown that 

 plants may be deprived of many of the chemical elements ordinarily 

 found, and no evil effects follow; but the absence of others has obvious 

 ill effects. Thus silica is an abundant material in the cell walls of the 

 epidermis of most cereals; yet corn has been cultivated through four 

 generations with practically no silica. 



Necessary elements. — A list of the elements that have been found in 

 the ash of one plant or another would be almost a list of the commoner 



