ROOTS AND RHIZOIDS 515 



they are relatively unbranched, but they branch profusely upon striking 

 the soil (fig. 739). Since monocotyls possess but a limited power of 

 diametral growth, a tree like the screw pine develops a top-heavy inverted 

 cone instead of a stable cone, as in dicotyls, so that its prop roots are 

 of great advantage in preserving equilibrium. In the banyan and in 



FIG. 741. The interior of a mangrove swamp, showing the prop roots of Rhizophora 

 Mangle together with arched roots that make a labyrinthine tangle near the ground; 

 Miami, Florida. Photograph by E. W. COWLES. 



other species of Ficus, roots issue from the horizontal branches and 

 grow directly downward to the ground. The support given by such 

 roots makes possible the enormous spread of the banyan. Many 

 species of Ficus (sometimes called strangling figs) usually begin life as 

 epiphytes, some of the roots developing in the dead bark and others 

 descending along the trunk to the ground. After a time all of the 

 nourishment comes from the ground, and the supporting tree is likely 

 to be strangled by an anastomosing network of enveloping roots or 

 borne down by the weight of the growing Ficus (fig. 740)- 



