656 BOWMAN— ECOLOGY AND 



Rhizophora, where the germinated seedHng stays on the parent 

 tree for nearly a year. Guppy^^* has put forth the unique view that 

 in a previous early geological age, under uniform warm, moist 

 climatic conditions and a very diffuse light due to constant cloudi- 

 ness, the viviparous habit was universal and that vivipary and the 

 conditions of the present mangrove swamp are an index both to 

 the meteorological conditions and to the forms of a very ancient 

 vegetation. The seedlings, being viviparous then, by evolution 

 through one of these processes presumably, although the w-riter 

 rather inclines to the former conclusion that the habit arose by small 

 beginnings, the dispersal of these depends on the ocean into which 

 they fall. 



The di'Spersal of the mangrove seedling has been discussed very 

 fully by several authors, at greatest length perhaps by Guppy, as 

 observed in the Fiji Islands and the Pacific, and more latterly in the 

 middle Atlantic coasts. This author regards the currents as the 

 source of dispersal, since in quiet water the seedling may drift for 

 months, but when they are buffeted by each other or floating objects 

 for any length of time, the plumule is injured and the seedling dies. 

 The present writer, nevertheless, has found many drifted seedlings 

 in the Tortugas which had been broken either at the plumule end or 

 the radicular end and in spite of these mutilations put forth adven- 

 titious buds at the lenticels at one end, or roots at the lenticels near 

 the radicular region. The nearest mangrove trees in this case were 

 those of the Marquesas atoll at a distance of twenty-five miles from 

 the Tortugas group. Intimately associated with the buoyancy of 

 the seedlings is their position in the water. Guppy noted that they 

 float vertically in fresh water and horizontally in salt water, while 

 they incline at various angles in dilutions of various densities. A 

 fortuitous agreement is seen in this relation between the specific 

 gravity of the seedling and the density of the water, for the hori- 

 zontal position keeps the plumule moist and uninjured by the fierce 

 sunlight. The seedlings have no buoyancy until the hypocotyl has 

 emerged from the fruit about six inches in the case of R. mucronata 

 and the same has been observed by the writer for young seedlings 



1^* Guppy, H. B., " Observations of a Naturalist in the Pacific," Vol. II., 

 Plant Dispersal, 1906, p. 470. 



