PHYSIOLOGY OF THE RED MANGROVE. 657 



of R. mangle. Guppy estimates that 95 per cent, of seedlings that 

 fall into the sea do float, and has further carried out a most interest- 

 ing series of experiments in England with seedlings brought from 

 the tropics and kept dry for five months. These experiments, which 

 show the prolonged vitality of the seedlings, recall the words of 

 Plutarch quoted in the first chapter of this paper, where he de- 

 scribed the " anacampserotes " as being plucked out of the sea and 

 hung up to dry, and which bud and put out green leaves presumably 

 when placed again in water. 



The manner in which reedlings come to take roots after having 

 journeyed for weeks in the ocean currents is also of interest to an 

 ecologist, because it is only on certain shores that the seedlings really 

 can eventually form a mangrove swamp. In the Tortugas and other 

 similar shores with wide beaches of coarse sand the essential condi- 

 tions are lacking and the seedlings go through a short life cycle 

 which the writer has reproduced under similar conditions at the 

 laboratory and always with the same result. The plants are dropped 

 from the trees in February, March and April in greatest number in 

 the thickets of the Marquesas, Boca Grande, or islands even further 

 east, these drift twenty-five to seventy-five miles westward with 

 the counter Florida current and the high spring tides carry them 

 up on the higher beach terraces formed in the coarse shifting sand 

 of the Tortugas with masses of Sargassum and the broken leaves 

 and rhizomes of Thalassia and Cymodocea which form long wind- 

 rows on the beaches. If there is sufficient of this debris to conserve 

 moisture during the dry summer months when it acts as sort of a 

 mulch for the Rhizophora seedlings, the little plants grow and the 

 plumule lengthens and forms several rather short internodes. These 

 may last with a desultory growth into late summer and perhaps be 

 all swept away from their bed in the shifting sands by the autumn 

 storms and hurricanes. As a rule, however, the seedlings are 

 buried more or less deeply in the sand with not sufficient debris, 

 since this flotsam is lighter and is flung a little farther back on the 

 beach than the seedHngs are. During the summer the plumule ex- 

 pands and the leaves put out, but these leaves never get over two 

 centimeters long and are soon burned up by the intense heat and 

 light of the glaring white beach and killed by the drying wind. 



