The Forms and Structures of Roots 



187 



are planted on levees. When roots of mesophytes grow in 

 water, they also develop air cavities in the cortex. 



Holdfast roots. CHmb- 

 ing plants, Hke the Vir- .^, 

 ginia creeper, poison ivy, ' 

 Boston ivy, and trumpet I 

 creeper, develop holdfast (' 

 roots which help to support > 

 the vines on trees, walls, • • 

 and rocks. By forcing their 

 way into minute pores and 

 crevices, they hold the 

 plant firmly in place. Usu- 

 ally the roots die at the 

 end of the first season, V 

 but in the trumpet creeper 

 they are perennial. In the z 

 tropics some of the large —' 

 climbing plants have hold- 

 fast roots by which they at- 

 tach themselves, and long, 



Fig. III. Holdfast roots of trumpet creeper, de- 

 COrd-llke roots that extend veloped from the nodes. These roots are perennial 

 downward through the air ^^^ ^^y lengthen and branch for several years. 



until they strike the soil and become absorbent roots. 



Epiphytes. A plant that lives perched on another plant is an 

 epiphyte (Greek: epi, upon, and phyton, plant). Mosses and 

 lichens are the most common epiphytes in temperate regions, 

 but in the rainy tropics and along our own Southern coast many 

 flowering plants five attached to the branches of trees. They 

 usually have leathery leaves and a Jow transpiration rate. Many 

 have water-storage tissue in fleshy stems or in thickened leaves. 

 Others are caUed tank epiphytes because they catch water in the 

 axils of the leaves or in pitcher-like leaves. Ephiphytes cling to 

 the supporting tree by means of roots that act both as holdfasts 



