DEPARTMENT OF MARINE BIOLOGY. 197 



The variations in numbers occurred at different periods of sampling. The 

 effect of shore conditions in shallow water is thus apparent, and was observed 

 previously by Drew in the Bahamas. 



The forms of bacteria, however, are not numerous in the tropical Pacific. 

 In the case of the uncontaminated ocean-water, not over five or six different 

 kinds of bacteria, so far as the medium in question is concerned, were found. 

 In all cases, moreover, including both the reef-water and that out at sea, one 

 dominant specimen of bacterium was always found in the medium in question, 

 which developed most rapidly and produced large colonies on the plates. 

 This organism has not yet been identified. 



Rose Island Notes. 



Studies were made on certain materials brought back by Mr. Mayor from 

 his trip to Rose Island in the Samoan group. The soil from Rose Island, 

 which is formed by the decomposition of highly calcareous material, resulting 

 in turn from the disintegration of lithotham.nium masses, contained an inter- 

 esting bacterial flora. The number of bacteria in this soil is not nearly so 

 great as in similar soil of greater age and under cultivation, but it appears 

 now, though only incomplete studies have been made, that some interesting 

 new forms of bacteria will be found. Some well-known old forms were en- 

 countered, among them Azotobader chroococcum. 



The surface crust of Rose Island, and of the atoll on which it is situated, 

 consists largely of lithothamnium, but underljing the loose mass of litho- 

 thamnium is a more compact limestone having very much the appearance 

 and (on a qualitative test) the composition of a dolomitized limestone. 

 On a quantitative analysis of that substance, however, it was found to consist 

 of 44.52 per cent calcium and only 6.98 per cent magnesium. This analysis 

 shows that the material is not fully dolomitized, but is probably in process of 

 being formed into dolomite. 



The surface rock from Rose Island is a loose and light substance into which 

 roots and decaying organic matter had penetrated. It was thought that that 

 material might contain large quantities of phosphoric acid and therefore be 

 valuable for fertilizer material. An analysis was therefore made of specimens 

 of this substance, and it was found to contain 12.05 per cent of phosphoric 

 acid. While this figure is very high for that kind of material, the quantity 

 of phosphoric acid is not high enough to make it pay to work the deposits as a 

 phosphate mine, especially considering the difficulties of transportation. 



Studies on Sea-Water Ph.enogams. 



With the object of determining whether the few rare species of flowering 

 plants growing in sea-water may possess some kej^ to the solution of the impor- 

 tant physiological problems of the absorption of salts from the growi:h medium, 

 it was determined to make a study of one of the interesting and remarkable 

 plants found at the edges of the reefs in the harbor of Pago Pago. This plant, 

 nearly related to Halophila ovalis, can be gathered at low tide from beneath 

 the sea-water and coral sand which covers most of it. Analyses are now being 

 made of that plant and of similar plants, which, it is hoped, may throw Ught 

 on some important phases of plant physiology. 



Experiments on the Rate of Growth of Sessile Marine Organisms other than Corals, 



hy F. A. Potts. 



The object of these experiments was the comparison of rates of growths 

 and dates of sexual maturity in animals of temperate and tropical seas respec- 

 tively. A body of facts has been accumulated for the former (c/. Orton, Proc. 



