PHYSIOLOGY OF THE RED MANGROVE. 661 



by the writer's own ecological notes along the Miami River, and 

 Guppy's observations in the Black River, Jamaica, show the fact 

 to remain that salt water is needed for the proper development of 

 a typical mangrove vegetation. The trees observed in the Ever- 

 glades and on other places in the interior of swamps having a fresh- 

 water substratum are of small size and poorly developed. 



To account for their origin and growth, even though poor, in 

 such interior swamps, it is logical to suppose that they have been 

 carried thither by currents flowing into the estuaries from the sea, 

 and for their continued existence we may suppose that the soil is 

 still sufficiently salt from previous inundations, or that the cur- 

 rents which carry the seedlings in are slightly brackish and so im- 

 pregnate the soil with a little salt. It is regretable that no data are 

 available on the salinity of the soils of such interior swamps where 

 mangroves are growing in this stunted condition. 



To return to the experiments made by the writer in the Miami 

 River and Biscayne Bay, it has been long known that in certain 

 estuaries there is an up-stream current of salt water which flows on 

 the bottom, while a down-stream current of fresh water flows on the 

 surface. In earlier observations along the Miami River, Arch 

 Creek, etc., the writer noted the gradual decrease in stature and 

 frequency of occurrence of mangroves as the river was ascended 

 until after three or four miles they had disappeared entirely. It 

 was supposed that this feature, which has often been remarked by 

 other ecologists, was in some way connected with the salinity of 

 the water, accordingly it was determined to make some top and 

 bottom hydrometer readings. To do this the launch Darzvin was 

 employed and the deep-sea water-sampling instrument taken from 

 the equipment of the institution's yacht, Anton DoJirn. This instru- 

 ment is a very ingenious device designed by Dr. Mayer and the late 

 Mr. Drew in the latter's work with bacteria in the sea water of the 

 Tortugas region. The instrument consists of a glass cylinder en- 

 closed in a heavy brass jacket. The top and bottom of the cylinder 

 are closed by means of brass plates, which fit tightly and are 

 operated by strong springs. The instrument is lowered into the sea 

 and on the yacht it is attached to the sounding machine and lowered 

 mechanically, and if samples are taken from deep sea water the 



