PHYSIOLOGY OF THE RED MANGROVE. 629 



A few cultures were also potted in a dark, bluish, gray mud taken 

 up from the bottom of the moat at Fort Jefferson on the adjacent 

 Garden Key. This mud, which seems very similar to that of typical 

 mangrove swamps, gets its dark color from decaying organic matter 

 in it and is also heavily charged with hydrogen sulphide arising 

 from the decomposition, just as is the ordinary mangrove swamp 

 mud. 



Some of this mud was boiled to drive off the gas and other 

 cultures were made of the unboiled mud to learn if there might be 

 a difference in the rate of transpiration. 



The water concentrations used in the soil experiments were pure 

 salt water and 50 per cent, salt water. 



Technique. 



The methods of getting at the rate of transpiration which 

 seemed the most feasible considering the available supply of ma- 

 terial was that of Stahl. This method, while only a colorimetric 

 method and hence not recognized as so exact as are perhaps volu- 

 metric methods, gave very interesting results with a few modifica- 

 tions to suit the conditions obtaining in the laboratory. A Ganong 

 leaf-clasp was used for the transpirometer. The indicators for this 

 little instrument are discs of Swedish filter paper saturated in 4 

 per cent, cobaltous chloride solution. These disc are inserted in the 

 rings inside the thin glass sides of the instrument which is then 

 clamped on a rod stand and the apparatus placed beside a culture 

 jar. Full-grown leaves of about the same size on plants of the 

 same age were used for tests. A small difficulty was encountered 

 in the high humidity content of an island and tropical climate 

 atmosphere, since the indicator discs necessarily had to be abso- 

 lutely dry. This difficulty was overcome by keeping the discs in a 

 calcium chloride desiccator of large size which conveniently held 

 the whole instrument with its ball-and-socket adjustable arm. In 

 making tests, the paper discs were placed in the clasp and dried 

 over an alcohol flame until the characteristic pink color of the paper 

 at ordinary atmospheric conditions was replaced by a deep blue of 

 absolute dryness. The whole clasp was then quickly placed in the 



