142 COLLEGE BOTANY 



The volatile oils are secretory products and differ from the 

 fats and fatty oils in being volatile but are also different chemi- 

 cally. They are the causes of the odors and flavors of many 

 plants, such as the peppermint, sassafras, spice bush, cloves, 

 cinnamon, cedar wood and orange rind. They also are the causes 

 of some of the odors in flowers and may be important factors in 

 attracting insects and assuring insect pollination. The oils of 

 these and many other plants are important commercial products 

 and are used extensively in the manufacture of perfumes and the 

 various essences used in the preparing of foods, medicines, etc. 



The resins are secretory products which are very similar to 

 the volatile oils. They are secreted very abundantly in the resin 

 tubes, which are formed in the wood of pines and other conifer- 

 ous trees. Pitch, turpentine, pine tar and rosin of commerce are 

 derived from pine resins. India rubber and gutta-percha are 

 manufactured from plant juices which are very similar to the 

 volatile oils and are obtained from many different plants. 



The enzymes are developed from the protoplasm of the liv- 

 ing cells and are similar in chemical composition to the proteins. 

 They have the power of causing chemical changes in other 

 compounds without being used up or undergoing any changes 

 which we can detect. They are found in both plants and ani- 

 mals, and are very important factors in the life processes of 

 the plant. Some of the more important are the diastases which 

 change starch into sugar, the invertases which change cane sugar 

 into dextrose and the proteoliitic which digest the proteids. 

 They may be divided into two groups: (1) the oxidase enzymes 

 which require oxygen and (2) the hydrolytic enzymes which 

 require water for their activities. 



Cell Wall. We have already learned that the cell wall is 



