40 VEGETABLE DRUGS WITHOUT ORGANIC STRUCTURE. 



The volatile oils are widely distributed in the vege- 

 table kingdom. The phanerogams or flowering plants 

 are particularly rich in them. From the cryptogams 

 volatile oils are known only from the male-fern, Dryopteris 

 Filix mas, and possibly from ergot. These oils are found 

 in the various organs of the plant, the leaves, stem, 

 flowers, fruits, and roots. The microscopical examina- 

 tion shows the oils to exist in special glandular structures, 

 either on the surface of the leaves, as in peppermint, or 

 in special secretory passages in the structure of the plant, 

 as in turpentine or in eucalyptus, etc. 



What function the volatile oils may serve in the plant 

 economy is a matter of much conjecture. They are 

 probably katabolic products so far as the metabolism 

 of the plant is concerned; but there is little doubt but 

 that in the case of many fruits their extreme pungency 

 is self -conservative to the plant, protecting it from the 

 ravages of insects, birds, and mammals. The biting 

 taste of many of the leaves also probably contributes 

 to their preservation from animal, notably insect, de- 

 struction. 



The volatile oils, it should first be impressed, are not 

 definite chemical compounds. They are complex mix- 

 tures of many substances belonging to many classes of 

 compounds. The volatile oil from one and the same 

 plant shows many variations in structure, according to 

 the part of the plant used, and radical differences in 

 the odor, physical properties, and physiological action 

 may be found in the oils derived from different organs 

 of a plant, the stem and the flowers, for instance. This 

 variation in chemical structure of many drugs is a car- 

 dinal principle. 



^-^olatile oils, however, are grouped under one generic 

 ttead because they are prepared in much the same manner 

 and because they possess many common physical and 

 chemical characteristics, and in so much as they are 



