Botanical Ecology of the Dry Tortugas. 119 



the key in 1904, according to statements of Dr. A. G. Mayer, the 

 Director of the Laboratory, and the aged appearance of the plants 

 supplements his statements. But in spite of these discrepancies, the 

 paper has been of great interest to the writer, and, as Millspaugh says 

 in a short introduction,^ p. 191 : 



"The principal value of the survey lies, therefore, first, in the historical 

 record of the present flora, which should enable futui'e students to determine 

 which species have come to the different islands since 1904 and which have 

 been unable to survive; second, in the knowledge of what species come first to 

 such microcosms, thus forming a basis upon which to judge of the ease or 

 difficulty of dispersion exhibited by certain species, and third, how and in what 

 conformation species spread when brought into an untainted environment." 



The paper has thus been of great value, to show what changes 

 have taken place in the flora of the Tortugas in the twelve years which 

 have elapsed since Mr. Lansing's survey — i. e., from 1904 to 1915. 



The writer spent the two summers of 1915 and 1916 at the Laboratory 

 in the Tortugas, taking field-notes, making some physiological experi- 

 ments on the plants, and working on the maps and collections of 

 herbarium material. The herbarium specimens have all been de- 

 posited in the Herbarium of the University of Pennsylvania. 



The scope of this paper has been confined to the Tortugas grou}) 

 because they are the most isolated of the Florida Keys and their flora 

 is strikingly different from that of the Marquesas, 25 miles to the east, 

 and also from that of the keys to the east of this latter atoll. The most 

 conspicuous feature of this difference is the absence of the mangrove 

 association to any considerable extent in the Tortugas, although Gar- 

 den Key has a few well-grown young trees which in the summer of the 

 writer's residence in the islands produced flowers and fruits. Another 

 reason was that while the writer had the opportunity and did visit and 

 take notes on the keys above, as well as west of Key West, the longer 

 periods spent in the Tortugas afforded much closer observation and 

 facilitated the securing of experimental data. His work on the other 

 keys was largely or entirely concerned with mangroves, some physi- 

 ological aspects of which have engaged his attention for several years. 



The distribution of species on the various keys of the group is illus- 

 trated by maps made in the field by the author with the aid of a plane- 

 table and sighting-rule. The outline map was made in the survey of 

 the group in 1914 and 1915 by Vaughan and Shaw.^ The various keys 

 will now be taken up separately and the species illustrated by symbols 

 on the distribution maps. A comparison is made in each case with 

 Lansing's survey. 



•Millspaugh, C. F., Flora of the Sand Keys of Florida. Field Columbian Museum, Publica- 

 tion 118, Bot. Series ii. No. 5. 



Vaughan, T. W., and E. W. Shaw, Geologic Investigations of the Florida Reef Tract. Car- 

 negie Inst. Wash., 1915, Year Book No. 14, p. 232. 



