140 PART II. VEGETABLE HISTOLOGY. 



them contain nitrogen in addition. Tannin (C 27 H 22 I7 ), salicin 

 (C 13 H, 8 7 ), coniferin C 16 H 22 8 ), convolvulin (C^H^O^), ericolin 

 C 3i H- M O n ), arbutin (C 25 H 34 O u ), daphnin C 31 H 34 ]9 ), menyanthin 

 (C^H^O,,), hesperidin (C 22 H 2fi O ]2 ), parillin (C u H 24 2 ), and saponin 

 (CsiHgeO^) are examples of the former, while amygdalin (C 20 H 27 

 NO n ) and laurocerasin (C^H^NO;;-)) are examples of the latter. 

 Some of them are acid in their reaction, while the majority of 

 them are neutral to test paper. They are, for the most part, 

 soluble in water. Many of them constitute active and important 

 medicinal principles. 



Compound Ammonias. These are complex bodies derived 

 from proteid matter in the course of the destructive changes 

 that are constantly taking place in the living plants, but beyond 

 this general fact little is known of their origin. They all contain 

 carbon, hydrogen and nitrogen and most of them, also, oxygen. 

 Chemically, they are either amines or amides. To this class of 

 compounds belong the 



Alkaloids. These are potent principles, some of them form- 

 ing the most valuable of medicines, and others the most dangerous 

 of poisons. Like the alkalies, they combine with acids to form 

 salts, and their solutions restore the blue color to reddened litmus, 

 whence the name, alkaloid. They are found in considerable 

 variety, though a single species of plant seldom produces more 

 than one or a few different kinds, and many plants do not appear 

 to possess them at all. It has not been ascertained that they are 

 of any service to the plant, except perhaps as a means of defense 

 against predacious animals and parasitic fungi. They may even 

 be injurious to the plants which produce them. The Poppy, for 

 example, may be poisoned by its own alkaloid, morphine. It is 

 perhaps for this reason that they are not commonly found in 

 large quantities in those parts of the plant where the vitality is 

 the greatest, but are accumulated in the less actively growing 

 parts of the bark, in fruits and in seeds, — parts destined sooner 

 or later to become detached from the plant, — and are thus 

 gradually gotten rid of. In the plant, we usually find them in 

 combination with organic acids. 



There are two groups, the non-volatile, which contain oxygen 

 and are solid at ordinary temperatures, and the volatile, which 

 do not contain oxygen and are liquid at ordinary temperatures. 

 The former are amides ; the latter, amines. 



