Ch. V, 8] SPECIAL FUNCTIONS OF ROOTS 255 



their stems large numbers of short roots, tough in texture 

 and adapted to dryness, which adhere at their tips to stones 

 or other supports (Fig. 180). In some tropical climbers, e.g. 

 species of Ficus (Fig. 181), elongated aerial roots grow out 



Fig. 179. — TwniophyUuni- Zollingeri, an epiphj'tic Orchid in which the 

 aerial roots have become flattened and have assumed the function of foliage. 

 A young flower stalk shows towards the left. (From Goebel.) 



horizontally, somewhat like tendrils, until they touch a 

 support, around which they turn thigmotropically, thus 

 securing a firm grasp ; and it is interesting to note that 

 such roots are able to saving in the horizontal plane by virtue 

 of a marked lateral geotropism. Aerial roots also occur 



