150 CHEMISTRY OF PLANT LIFE 



the same physiological function, if indeed any of them actually 

 have any such function. 



It is evident that those aromatic compounds which occur as 

 normal secretions of plants and which give to the plants their 

 characteristic odors may act either as an attraction to animals 

 which might utilize the plants as food and so serve to distribute 

 the seed forms, or as a repellent to prevent the too rapid destruc- 

 tion of the leaves, stems, or seeds of certain species of plants whose 

 slow-growing habits require the long-continued growth of these 

 portions of the plant for the perpetuation of the species. The 

 presence of these compounds in larger proportions in those species 

 of conifers, etc., which grow in tropical regions, in competition 

 with other rapid-growing vegetation, suggests the latter possibility. 

 It must be admitted, however, that their presence in such cases 

 may be the result of climatic conditions, as indicated by the fact 

 that most spice plants are tropical in habit, rather than the result 

 of then- protective influence in the struggle for survival during past 

 ages. 



Many of the oils and resins which are secreted as the result of 

 injury by disease or wounds have marked antiseptic properties 

 and undoubtedly serve to prevent the entrance into the injured 

 tissue of destructive organisms. 



But apart from these possible protective influences which 

 may have had an important effect upon the preservation and 

 perpetuation of the species of plants which secrete them, there is 

 no known biological necessity for the presence of these aromatic- 

 substances in plants. 



REFERENCES 



ABDERHALDEN, E. " Biochemisches Handlexikon, Band 7, Gerbstoffe, 

 Flechtenstoffe, Saponine, Bitterstoffe, Terpene, Aetherische Oele, Harze 

 Kautschuk," 822 pages, Berlin, 1912. 



ALLEN'S Commercial Organic Analysis, Vol. IV, "Resins, Rubber, Gutta- 

 percha, and Essential Oils," 461 pages, 7 figs., Philadelphia, 1911 (4th 

 ed.). 



HEUSLER, F. trans by POND, F. J. "The Chemistry of the Terpenes," 457 

 pages, Philadelphia, 1902. 



PARRY, E. J. "The Chemistry of Essential Oils and Perfumes," 401 pages, 

 20 figs., London, 1899. 



