108 A TEXTBOOK OF BOTANY [Cn. Ill, 13 



bons, or else contain also some oxygen, being formed without 

 doubt from carbohydrates. Their pleasant odors and tastes 

 are utilized by man in perfumes and essences, though in 

 recent times he has been able to dispense with the plants, 

 and manufacture a great many in his own chemical labora- 

 tory. But they will always continue to add charm to our 

 gardens. 



Related to the essential oils are some other substances of 

 considerable importance, of which the most important are 

 resins, camphor, and caoutchouc. Resins, known to us in 

 balsam, rosin, pitch, and spruce gum, are formed mostly in 

 special passages, and are particularly abundant in the 

 Coniferse or Pine Family; but we know little as to their 

 significance, whether functional or incidental. Man utilizes 

 their imperviousness to water in various ways. A fossil 

 resin is amber. Camphor is a gum of -a special tree, again 

 of unknown significance, and having well-known uses by 

 man. Caoutchouc, the basis of rubber, is formed by many 

 plants, usually in their "milk" (or latex), though its meaning 

 to the plant is uncertain ; but the uses that man makes of 

 its wonderful tenacity and elasticity need no description. 



THE PIGMENTS are the substances which give the bright 

 colors to the various parts of plants. They are very diverse 

 in chemical' composition (often including elements addi- 

 tional to those of carbohydrates and proteins), and in 

 significance to the plant. Thus chlorophyll (composition 

 C5 4 H7 2 06N 4 Mg) has a function already familiar to the stu- 

 dent, while the ever-associated xanthophyll (composition 

 C4oH5 6 2 ) and carotin (CIoHse) have, no doubt, a function, 

 though it is unknown. Anthocyanin, called descriptively 

 erythrophyll (composition, in a typical case, the Cranberry, 

 C 2 iH 2 20i2) is the basis of the reds, purples, and blues in 

 plants, yielding red with acid cell sap, and blue with alka- 

 line. In flowers these and other pigments help to guide in- 

 sects, and in fruits other animals, for functional reasons 

 later to be noted ; but in other cases they seem to represent 



