PHYSIOLOGY OF THE RED MANGROVE. 659 



obtain as Key West, measurements here of trees which were repre- 

 sentative of all the trees about the lower Florida Keys showed the 

 average tree to be 3-4 meters, growing on oolite with only 2-5 centi- 

 meters of mud covering the absorptive roots (Fig. 6, PI. VIII.). 

 These absorptive roots were 20-40 centimeters long and 1-2 centi- 

 meters in diameter, while the prop to which they were attached was 

 of an average length of 1.8 meters, the shoot of the props being 

 about 1.5-2 meters. The hydrometer seedlings for the water here, 

 on June 25, was sp. gr. 1.0205 at 34° C. On June 5, at the same 

 place where seedlings were grown off shore in 20 cm. of water, the 

 seedlings were almost similar; T. 34° C. and sp. gr. 1.021. 



At Boca Chica, the conditions were slightly different, the ob- 

 servations made on June 9 at low tide. The trees were growing 

 in deep mud almost a meter deep and were about five meters tall, 

 the roots being covered, at low tide, with 10-20 cm. of water. 

 Hydrometer seedlings here showed a sp. gr. of 1.0235 at 30° C. 

 On this island also were seen Rhisophora trees growing five to eight 

 meters in shore in apparently dry shell sand, in a healthy condition 

 (Fig. 5, PI. VIII.). 



At Cayo Agua on June 17 and 24 about the same measurements 

 were made as at Boca Chica, except that here trees were found full 

 of flow^ers and fruits at all stages as well as pendant seedlings. At 

 no other island in the lower keys were flowers noted at this time 

 of the year. On the west side of the island a hurricane of a previous 

 winter had broken and washed up a considerable area of the swamp, 

 and in this close mass of dead and white bleached twigs and 

 branches, the ideal situation seemed to be afforded to the young 

 seedlings to start growth. The dead twigs overhead provided a 

 lattice of the right sort for optimum light intensity, while the decay- 

 ing branches in the mud below offered quiet water and debris for 

 anchorage. The same thing was seen in the hurricane damaged 

 swamp at ^Marquesas (Fig. 2, PI. VIII.). 



At Mangrove Island, Crawfish Key and Ragged Keys trees five 

 to six meters high were observed growing in deep mud. At the 

 last mentioned keys the mangroves were associated with Avicennia, 

 Conocarpus and Laguncularia. At Bahia Honda and Duck Island 

 only the inner or Gulf side of the islands have a mangrove fringe 



