THE BIOLOGIST POSES SOME PROBLEMS 87 



history a diameter of the order of 100 m/x. Some microbiologists 

 regard these organisms as degenerate Eubacteriae, others place 

 them as an independent group. 



When we consider the broad environmental requirements of 

 the Monera we find that in general they are organisms living at 

 solid-liquid or liquid-gas interfaces in a great variety of circum- 

 stances, in soils, aquatic sediments, on suspended tripton, or as 

 epiphytes, commensals, symbionts, or parasites. Only in the 

 photosynthetic groups do massive populations develop as plankton 

 in the free water. On the whole, the major groups show little 

 specialization into freshwater or marine organisms. In many genera 

 in the Eubacteriae and the Myxophyceae and in some of the few 

 genera of the smaller groups marine forms occur and these are 

 often easily adapted, apparently by an evolutionary process in- 

 volving few mutations, to freshwater or very euryhaline life. 

 Specific marine genera occur only in a few orders, such as in the 

 Pleurocapsales among the blue green algae, and these are not 

 primitive. So far organisms like Sapromyces appear to be known 

 only from nonmarine environments, though various problematic 

 fouling organisms are recorded from the sea, some of which may 

 prove to be very unspecialized. Any genus containing both fresh 

 and salt water species is obviously able to go from one environment 

 to the other by a series of genetic changes not greater in number 

 than is required to make a species. Within the bacteria many cases 

 are known from the monumental work of ZoBell (1946) where such 

 changes take place over a quite short period of time, presumably 

 within the species. Little is known of the physiology of the processes 

 involved in genetic adaptation of this sort, but the work of Pratt 

 and Waddell (1959) suggests that ultimately much can be learnt 

 of the mechanisms involved. All organisms within a restricted 

 taxon showing this kind of diversity will be regarded as exhibiting 

 evolutionary euryhalinity to a greater or less degree. 



W^e are evidently justified in concluding that evolutionary 

 euryhalinity is characteristic of a great variety of Moneran lines. 

 Where there is a suggestion of a more stenohaline history it is 

 reasonably certain that the sea is not more favored than non- 

 marine environments; possibly it is less favored. 



When we leave the Monera we find great difficulty in deciding 



