282 LEAVES 



The volatile oils differ not only chemically from fatty oils, but 

 also in being volatile. They cause most of the odors of plants. 

 Oil of Peppermint, Sassafras, Cinnamon, Cloves, Cedar, and the 

 oil of the Orange rind are familiar volatile oils. A number of 

 uses to the plant have been assigned to the various volatile oils, 

 such as protection against destructive organisms, attraction of 

 insects in the pollination of flowers, and serving as a storage form 

 of food. Their pleasant odors and tastes add charm to the 

 flowers of many garden plants, and before the chemists learned 

 to make many of them, plants were our chief source of the per- 

 fumes and essences of commerce. Their composition suggests 

 their origin from the photosynthetic sugar, since nearly all of 

 them contain only carbon and hydrogen, or only carbon, hydrogen, 

 and oxygen. 



Closely related to the volatile oils are a number of substances, 

 such as the Pine resins, 'india rubber, gutta percha, camphor, and 

 asafetida, which are important commercially, although their use 

 to the plant is not definitely known. From the Pine resins, which 

 are found in the resin ducts of Pines, turpentine, pine tar, rosin, 

 and pitch are obtained. India rubber is the prepared milk-juice 

 obtained from a number of trees of tropical countries. Gutta 

 percha, used in making surgical instruments, in filling teeth, and 

 in a number of other ways, is obtained also from the milk-juice 

 or latex of a number of plants. Camphor is obtained from a 

 number of tropical trees and asafetida from a group of herba- 

 ceous plants. 



Glucosides are complex substances and are so named because 

 many of them contain glucose as one of their constituents. They 

 may be considered storage forms of food since they yield a sugar 

 when broken down. Amygdalin, the bitter substance in the 

 seeds of the Bitter Almond, is one of the best known glucosides. 

 Its formula is C 2 oH 2 7NOn, and when decomposed it yields glu- 

 cose (CeH^Oe), hydrocyanic acid (HCN), and benzaldehyde 

 (C 6 H 5 CHO). Glucosides vary much in composition and con- 

 sequently in the products which they yield when decomposed. 

 Thus the glucoside coniferin (Ci 6 H 2 2O 8 ), found in coniferous trees 

 and Asparagus, yields glucose and coniferyl alcohol (CioH^Os) 

 when decomposed. 



Glucosides occur in all parts of the plant and are especially 

 abundant in the parenchyma cells of roots, stems, and leaves. 



