GULF OF MEXICO 



231 



the Gulf frequently are found in silica poor waters, 

 while larger heavy-shelled forms {/ihizosolenia, 

 Coscinodiscus, Biddulphia sp.) sometimes found 

 in cooler, northern waters, are not present in the 

 tropical or subtropical plankton unless reduced in 

 size or weight of then- silica shells. These obser- 

 vations are general and at present not based on 

 extensive quantitative measurements whidi, how- 

 ever, are being planned by the author. 



Further observations by the wi-iter, although 

 not quantitative, stronglj' suggest that wherever 

 there is a substantial influent of silica-bearing 

 water, the diatom growth is both more abundant, 

 and the cells (and their shells) are of a more robust 

 character. Such a condition was noticed, for in- 

 stance, at Tortugas in close proximity to the 

 crumbling walls of siliceous brick of old Fort 

 Jefferson, washed on all sides by the shallow cal- 

 careous water. In the moat and in semicnclosed 

 pools adjacent to these walls a very heavy growth 

 of Tropidoneis lepidoptera and other diatoms was 

 noted. The more extensive result of such rela- 

 tions, however, is to be seen in areas influenced 

 by the discharge of river systems that drain argil- 

 laceous soils, or in the inshore waters affected by 

 the run-off from steeper siliceous terrain, such as 

 found around the coast of Cuba, the west coast 

 of Florida and the coast of Alabama. Waters of 

 such constitution support heavy growths of robust 

 shelled diatoms as Terpsinoe musica, Biddulphia 

 pulchella, Hydrosera triquetra, Lithodesmium, and 

 others. 



The contrast of the rich diatom flora produced 

 in such an envu-onment with the frail and delicate 

 plankton forms of the silica-poor calcareous waters 

 about Tortugas, for example, appears to be a 

 demonstration of a point long suspected by the 

 writer that a plentiful supply of silica greatly 

 enliances the growth of diatoms. Evidence from 

 other regions and types of habitat, in the writer's 

 experience, supports this contention. Where richer 

 waters with a higher silica content occur in tropical 

 i-egions owing to cold currents, upwelling, or run-off 

 from siliceous soils, a heavy diatom productivity, 

 with oftentimes more robust individuals is the 

 result. 



The relation of diatom growth to silica content 

 of sea water is imdoubtedly significant but not too 

 well understood. The varied conditions of the 

 Gulf of Mexico afford good opportunity for such 



study. The effects of phosphates, nitrates, and 

 other nutritive elements should be examined coor- 

 dinately although it does not appear from the 

 present observations that they could be confused 

 with the role of silica as a limiting factor. 



BIBLIOGRAPHY 



Bailey, J. W. 



1844. Review of Ehreriberg's Verbreitung und Einfluss 

 der mikroskopischcii LebeiKS in SUd- und Nord- 

 Amerika. Am. .Jour. Sci. and Arts 46: 297-3 IH. 

 BOYER, C. S. 



1926. Synopsis of North American Diatomaceae, Part 



I. Coscinodiscatae, Rhizosolenatae, Biddulphiatae, 

 Fragilariatae. Proe. Acad. Nat. Sci. Philadelphia 78 

 (Supp.): 1-228. 



1927. Synopsis of North American Diatomaceae, Part 



II. Xaviculatae, Surirellatae. Proc. Acad. Nat. Sci. 

 Philadelphia 79 (Supp.) : 229-583. 



Cleve, p. T. 



1878. Diatoms from the West Indian Archipelago. 



Bihang. Kongl. Svenska Vetenskaps-Akad. Handl. 5 



(8): 1-22, pis. 1-5. (Translated into French, with 



plates, by J. Pelletan in: Jour, de Micrographie, 1879.) 



Cox, J. D. 



1901. .\lgae. In: C. Mohr, Plant Life of .Alabama. 

 Contr. U. S. Nat. Herb. 6: 142-148. 



Cunningham, K. M. 



1889. The diatoms of Mobile, Alabama. The Micro- 

 scope 9 (4): 10,5-108. 



Ehrenbebg, C. G. 



1841 (1843). Verbreitung und einfluss der mikroskopi- 

 schen lebens Slid- und Nord-Amerika. (On the ex- 

 tent and influence of microscopic life in South and 

 North America. With a list of the diatoms.) 

 Abhandl. Konigl. Akad. der Wissenschaften zu 

 Berlin, March 25 & June 10, 1841: 291-446, pis. 1-4 

 (colored). (Reviewed with extracts, by J. W. Bailey: 

 Am. .lour. Sci. and Arts 46: 297-313. 1844.) 

 1842. On the extent and influence of microscopic life in 

 South and North America. (With a list of the 

 diatoms.) Microsc. Jour, and Struct. Record 2: 24-. 

 (From: .\bhandl. Konigl. Akad. der Wis.senschaften 

 zu BerUn, 1841.) 



Greenleaf, R. C. 



1866. On the diatoms and other microscopic objects 

 found in soundings from the Gulf of Mexico, between 

 Sand Key and Elmoro, made by Henry Mitchell of 

 U. S. Coast Survey. Proc. Boston Soc. Nat. Hist. 

 11: 79. 



Greville, R. K. 



1857. Description of some new diatomaceous forms from 



the West Indies. Quar. Jour. Microsc. Sci., 5: 7-12, 



pi. 3. 

 1866. Descriptions of new and rare diatoms from the 



tropics and Southern Hemisphere. Trans. Bot. Soc. 



Edinburgh 8: 436-441, pi. 6. Edinburgh New 



Philosophical Jour., 1866. 



