200 CARNEGIE INSTITUTION OF WASHINGTON. 



Report on Botanical Work at the Tortugas Laboratory for the Season of 1915, 



by H. H. M. Bowman. 



The primary object of my going to the Tortugas Laboratory was to investi- 

 gate the physiology, ecology, and other points in the life history of the red 

 mangrove, Rhizophora mangle, and to some extent of the black mangrove, 

 Avicennia nitida. A good beginning has been made, and during several weeks 

 spent at Key West important data were secured on the rooting habits of both 

 genera and the requirements and adaptability of the trees to various kinds of 

 bottoms and solid media of growth. Some attempt was also made here to 

 get a correlation between the distribution of the plants and the salinity of the 

 water; this data has not as yet been worked out. Notes were also taken and 

 water collected at a few of the upper Florida keys. The work on the distribu- 

 tion of the mangrove along the east coast of Florida has barely been glanced 

 at during this season, but plenty of material was secured for morphological and 

 histological studies to be pursued this winter. 



At the Tortugas Laboratory a series of experiments was carried on with 

 Rhizophora and some interesting curves were obtained for the transpiration 

 of these plants under different conditions — e. g., waters of various degrees of 

 concentration and soils of different character. These experiments will be 

 pursued with some variation in the methods of handling the plants next season, 

 when it is hoped some practical difficulties can be overcome with the light of 

 the experience gained this summer. 



As secondary objects of study, mention may first be made of the curious 

 spermatophyte which was brought up in dredging expeditions from water over 

 17 fathoms deep. The study of this plant promises to be interesting in its 

 probable bearing on recent geological theories concerning the formations in 

 this part of the Gulf of Mexico. 



Another feature of this season's work was the botanical ecology of the Tortu- 

 gas Group, which will be published as a special contribution. Lastly, a note 

 may be given of a variation in Conocarpus erecta L., which was found at Fort 

 Jefferson on Garden Key of the Tortugas a few days before the season closed. 



Studies on Alcyonaria, by L. R. Cary. 



Photographic records and measurements of gorgonian colonies cemented 

 on tiles were continued during the present season. The results obtained con- 

 firm my previously published conclusions that the growth of all the common 

 species of gorgonians, with one or two exceptions, is very slow after three years. 



On the southern end of White Shoal, where, as stated in my report for last 

 season, the bottom had been swept clean of all gorgonians by the hurricane 

 of October 1910, the character of the gorgonian fauna has undergone a notice- 

 able change within the last year. In July 1914 at least 95 per cent of all the 

 gorgonians present were of the single species Gorgonia acerosa, practically all of 

 which were of a size which indicated that they were about two years old. In 

 July 1915 a considerable number of colonies of other species of gorgonians were 

 found on the same reef area, together with many young colonies of G. acerosa 

 which had become attached during the breeding-season of 1914. Over a 

 large portion of this recently barren reef a luxuriant growth of gulf weed 

 {Sargassum bacciferum) had become established, while in many small patches 

 all sedentary animals have been destroyed by the algae. 



The Alcyonaria as a Factor in Reef Limestone Formation. 



The figures used as the basis for the estimates of the amount of calcium 

 carbonate held as spicules in the tissues of the gorgonian colonies on any area 

 of reef bottom in the region about Tortugas, which were published in the Year 



