266 NITROGEN BASES 



aceae and Solanaceae stand out in the provision of several of 

 these substances. The Labiatse, Rosaceae, Orchiclaceae, and 

 Monocotyledons and Gymnosperms very rarely contain them. 

 Alkaloids may occur in solution in the cell sap, especially 

 in young parenchyma : in older tissues the substances in ques- 

 tion may be stored in the solid state. They are found in the 

 seeds and fruits more particularly, but in the case of the alka- 

 loids of the Solanaceae and some other plants they occur in 

 the leaves, whilst the roots are the chief sources of the alka- 

 loids of Acon&um, Corydalis, and Hydrastis. The cinchona 

 alkaloids, and also pelletierine of the pomegranate, are con- 

 tained in the bark of their respective trees. 



Classification. 



The classification of the alkaloids is based upon the struc- 

 ture of the nucleus upon which their molecules are built up. 

 Five groups of alkaloids are accordingly recognized. 



I. Pyridine Alkaloids. These, as the name implies, are 

 all derivatives of pyridine, and include : 



Coniine from Conium maculatum. 



Arecolin from Areca catechu. 



Trigonellin from Trigonellum fcenum, Pisum sativum, etc. 



Piperine from Piper, and 



Nicotine from Nicotiana tabacum. 



Some idea of the structure of the molecules of alkaloids 

 belonging to this group may be obtained from the two following 

 constitutional formulae, which represent coniine and nicotine 

 respectively : 



CH 2 CH CH 2 CH a 



/ \ / \ I 



CH 2 CH 2 CH C CH CH 2 



CH 2 CHCH.jCH 2 CH 8 CH CH N 



\ / V / 



NH N CH 3 



Coniine Nicotine 



From these formulae it may be seen that coniine is derived 

 from pyridine, or more strictly from piperidine 



CH 2 



/ \ 



CH 2 CH 2 



CH, CH, 



\ / 



HN 

 Piperidine 



