[BERKELEY] MARINE BACTERIA 21 



growth in any medium being obtained from these samples at 28°C. 

 This is not surprising seeing that the temperature is some 20" above 

 that of the natural habitat of the organisms.^ Colonies were visible 

 on the plate inoculated with surface water after 2 days. In 3 days 

 six surface colonies had developed which appeared to be of three kinds. 



(i) Round, white, fiat, denser at centre than at edge, undulat- 

 ing edge, mottled surface (Culture II). 



(ii) Round, white, flat uniformly dense throughout, entire 

 edge, finely granular surface. (Culture III). 



(iii) A type intermediary between (i) and (ii). (Culture IV). 



A granular deposit of calcium carbonate was visible in the medium 

 surrounding all the colonies of these types after 4 days. In ten days 

 the colonies of types (i) and (iii) had acquired a very characteristic 

 appearance. They were now about 3^ in. in diameter, were consider- 

 ably raised from the medium and were dry and wrinkled. The centre 

 of the colony was thicker and darker than towards the edges and the 

 wrinkles radiated from this dark area nearly to the edge. The colonies 

 of type (ii) had increased in size but had not altered appreciably in 

 character. 



Two additional types of colony had now developed: — 



(iv) Round, semi-transparent, moist, greyish, entire edge, 



domed with depression at centre (Culture V). 



(v) Round, pale yellow, flat, dry, entire edge (Culture 



XXVIII). 



Several submerged colonies of indeterminate type also developed 

 on this plate: 15 colonies in all were counted. 



1 In the case of agar plates it must be remembered that the bacteria are called 

 upon to withstand a temperature of at least 40°C. during inoculation, since the agar 

 solidifies a few degrees below this temperature. Probably for this reason no satis- 

 factory results were obtained by plating cultures containing bacteria obtained from 

 20 to 100 fathoms during the whole course of this work. In cases where growth was 

 very active at air temperature in liquid media or smear cultures no colonies were 

 obtained on plating, even if the plates were kept at the same temperature. Drew 

 draws attention to the sensitiveness of marine bacteria to heat in the paper to which 

 reference has already been made. This may account in some measure for the marked 

 falling off in numbers of bacteria found by him in the waters of "Tongue of the 

 Ocean" at about 350 fathoms (pp. 35 and 36), the temperature of the water at this 

 depth in the Florida seas approximating to that at 20 fathoms in the case dealt with 

 in this paper. Gelatin media would probably be found to give more satisfactory 

 results in dealing with bacteria drawn from environments in which such tempera- 

 tures prevail. 



