THE ANG 10 SPERM AE : ROOTS 815 



and their function seems to be only that of giving more secure anchorage 

 in the soil against the effects of wind on the large aerial shoots. 



(c) Buttress Roots. 



Many tropical trees show remarkable buttress roots around the base of 

 the trunk. They are formed by the bases of the main roots, in which secondary 

 thickening is unsymmetrical, being chiefly on the upper side. This results 

 in the formation of thick, woody walls, running obliquely between the trunk 

 and the ground (Fig. 812). They are sometimes so large that two men, 



Fig. 812. — Eriodetidron aiifractuosum. Tree showing buttress roots with horizontal growth- 



{From a photograph lent by the University of Florida, U.S.A.) 



Standing one on each side of a buttress, would be hidden from each other. 

 Some authors have suggested that this additional support of the trunk is 

 rendered necessary by the great height of many tropical trees and perhaps 

 by the prevalence of hurricane winds, but this is largely guesswork, 



{d) Horizontal Roots. 



A common habit among tropical trees is the production of roots which 

 grow horizontally along the surface of the soil, spreading widely around the 

 tree. Although they are a marked feature of tropical forests, it is not possible 

 to say what advantage, if any, is gained by this method of growth. 



{e) Aerial Roots. 



Aerial roots are produced by most plants which grow as epiphytes 

 (see Volume IV.). In many cases these roots may be of enormous length and 



