ROOTS: DEVELOPMENT AND STRUCTURES 



297 



[Chap. XXIX 



Mature corn plants in the field usually have "prop roots" that have 

 developed from the lower nodes above the ground. Pandanus, mangro\e, 

 and other tropical trees like the banyan and fig, have adventitious roots 

 from the main trunk and also from the lateral branches of the crown 

 (Figs. 115-118). When these so-called "prop roots" and "drop roots" 



Fig. 115. Prop roots of pandanus, a tropical shore plant, planted in Florida. Plroto 



by W. Fifield. 



have grown into the soil, they become additional supports and have the 

 same relation to the soil as primary root systems. 



Many vines, such as the Virginia creeper, English ivy, poison ivy, and 

 trumpet creeper, have aerial roots which become attached to the trunks 

 of trees, walls of buildings, or rock cliffs, and anchor the slender shoots 

 far above the height to which the stem can support itself. Orchids, 

 bromelias, and many ferns in the tropics live as epiphytes, that is, perched 

 on the branches of trees and shrubs (Fig. 119). These plants also have 

 aerial roots which form masses below the leaves and not only attach the 



