PHYSIOLOGY OF THE RED MANGROVE. 633 



sulphide gas was of course due to the higher concentration of the 

 acid sokition, the ionization being H -(- and HS — . In cultures of 

 which the mud had been previously boiled to drive off the gas, the 

 ultimate death of the plant was only postponed as the further de- 

 composition of the organic substances in the mud soon produced 

 enough HoS to again render the culture toxic. It is presumed that 

 the constant action of the waves and the daily tides so dilute the 

 gas in the natural mangrove beds that the toxicity is removed. 

 Many factors enter into this question, as the precipitation of sul- 

 phides by the inter-action of bases in the sea water, action of the 

 products of denitrifying basteria in large quantity in the tropical 

 waters and other complex chemical phenomena. On account of the 

 early death of the plants no records could be made of these cul- 

 tures, or at least in sufficient number to warrant any definite con- 

 clusions. All the cultures were allowed about three weeks to adjust 

 themselves to the changed conditions in the laboratory from those 

 of their natural beds, before any records were taken. By this ad- 

 justing process time was also given to eliminate any seedlings which 

 were not healthy or showed signs of not reacting normally. 



Lastly a series of two hundred young trees was planted on a 

 small mound of mud in the moat at Fort Jefferson during the sum- 

 mer of 1 91 5. The top of this little mound of debris was only 

 moistened at the highest tide and this exposed part was largely com- 

 posed of coarse broken corals and shells, pieces ten to fifteen centi- 

 meters in dimension. The little plants about one half meter high 

 were set at varying levels on the mound, some on top in the dry 

 coarse debris and the lowest almost submerged even at low tide. 

 In 1916 on the writer's return to Tortugas only twelve of these trees 

 were alive, the winter storms had so disturbed the mound that many 

 were washed away, the remaining ones were growing and apparently 

 in good condition. The significance of the experiment will be con- 

 sidered under the ecological relations. 



Transpiration Records. 

 The result of about two thousand records made in both seasons 

 of the years 1915 and 1916 are now set forth. The intervals be- 

 tween the stop-watch registrations were all calculated for each test, 



