34 



MOEPHOLOGY OF THE ROOT. 



into which they penetrate. More remarkable cases abound in 

 those tropical regions where the sultry air, saturated with moist- 

 ure for a large part of the year, favors the utmost luxuriance of 

 vegetation. In the Palm-like Pandanus or Screw-Pine * (Fig. 

 69), very strong roots, emitted in the open air from the trunk, 



and soon reaching 

 the soil, give the 

 appearance of a tree 

 partially raised out 

 of the ground. The 

 famous Banyan-tree 

 of India (Fig. 71) is 

 a still more striking 

 illustration ; for the 

 aerial roots strike 

 from the horizontal 

 branches of the tree, 

 often at a great 

 height, at first swing- 

 ing free in the air, 

 but finally reach- 

 ing and establishing 

 themselves in the 

 ground, where they 

 increase in diameter 

 and form accessory 

 trunks, surrounding 

 the original bole and supporting the wide-spread canopy of 

 branches and foliage. Very similar is the economy of the Man- 

 grove (Fig. 70) , which forms impenetrable thickets on low and 

 muddy sea-shores in the tropics throughout most parts of the 

 world, extending even to the coast of Florida and Louisiana. 

 Here aerial roots spring not only from the main trunk, as in 

 the Pandanus, but also from the branchlets, as in the Banyan. 

 Even the radicle of the embryo starts into growth, protrudes, 

 and attains considerable length while the fruit is still attached to 

 the branch. 



59". Aerial Rootlets for climbing are familiar in the Ivy of the 

 Old World (Hedera) , Trumpet-Creeper (Tecoma radicans) , and 

 our Poison Ivy (Rhus Toxicodendron) ; by the adhesion of 



1 So named, not from any resemblance to a Pine-tree, but from a like- 

 ness of the foliage to that of a Pine-Apple. 



FIG. 69. Pandanus, or Screw-Pine; and in the background, 70, a Mangrove-tree 

 (Rhizophora Mangle). 



