ALONG THE MANGROVE SHORE 257 



A mangrove forest advances into shoal water by 

 means of its arching roots and the young plants 

 which spring up in very shallow places. The roots 

 do not merely drop into the mud and take hold 

 but they often continue to grow on, arching over 

 and over, and extending for thirty or forty feet. 

 Others drop from the branches twenty feet above 

 and make fast in the mud. Occasionally a hori- 

 zontal limb drops a root which fastens in the mud, 

 after which the original tree dies and the new root 

 becomes a tree, or the new may eventually become 

 separated from the parent and both live inde- 

 pendently. 



In the economy of the tree the roots have a four- 

 fold function. First, — they render the ordinary 

 service of bringing up crude sap like all conven- 

 tional roots. Second, — they act as pneumato- 

 phores or oxygen gatherers and pumps. The soil 

 in swamps, as I have elsewhere said, is lacking in 

 oxygen, and trees living in them must resort to 

 special devices to obtain it. The mangroves do 

 this by exposing a great mass of roots to the atmos- 

 phere. Third,— they elevate the body of the tree 

 well above standing water, for if the bases of these 

 semi-aquatic trees were constantly submerged it 



