The Various Substances Made by Plants 125 



waste none. To this end they even go so far as to remove from 

 their leaves, before these are dropped, such of the nitrogenous 

 and other compounds as can be used economically again. Unlike 

 animals, they excrete no nitrogen, or extremely little, in either 

 solid, liquid, or gaseous form, but conserve it with care and use 

 it over and over again; so that it is only released in the end by 

 their decay after death. 



Class V. The Principal Poisons, or Alkaloids 



These substances are notorious as including the most violent 

 plant poisons. Thus strychnine (from the Strychnos bean), 

 nicotine (from the Tobacco leaves), morphine (from the milky 

 juice of Poppies) are alkaloids, as is the poison, muscarine, of the 

 deadliest jVIushrooms. Some alkaloids, while not poisonous, 

 have strong properties in other respects, such as quinine, obtained 

 from the bark of the Cinchona tree and efficacious in breaking up 

 fevers; caffeine, the stimulating substance in Tea leaves and Coffee 

 berries; cocaine from Cocoa seeds, the well knoTvn local anaesthetic 

 and fatally-alluring drug. Their meaning in the plant is uncer- 

 tain, and all the more puzzling since they mostly are poisonous 

 to the very plants which produce them if injected into other 

 parts of their tissues. Nor is it certain just how they produce 

 their poisonous effects. Alkaloids occur also in animal tissues 

 as a product of the processes of fermentation and decay; they are 

 called ptomaines, and are very deadly, being the real cause of 

 death in bacterial diseases. Chemically the alkaloids are related 

 to the amides, from which they are no doubt formed, not at all 

 as a step in the formation of proteins, but as a side group. A 

 typical formula is that of caffeine, CsH^qOoN^. 



It has recently been discovered that the roots of our common 

 field crops appear to excrete into the soil minute quantities of 

 substances poisonous to the plants which produce them; and it is 

 probable that the presence of such substances, and not the ex- 

 haustion of the necessary mineral matters, is the real cause of 



