THE LEUCO-THIOBACTERIA 99 



(c) The approximation of the size to that of the normal 

 bacterial endospore in the genus bacillus. 



Their germination has not been observed. 

 Sexual reproduction apparently does not occur. 



Species of the Genus Beggiatoa. 



When many individuals of Beggiatoa are observed in the 

 same microscope-field, threads varying in thickness from i^ 

 and less to approxim.ately 3/x are found, and a similar variation 

 is to be found in the lengths of the cells in the threads. 



Winogradsky (2) has arbitrarily fixed on certain ranges of 

 size in such a mixture and given a specific name to each selected 

 range. He distinguishes different species in accordance with 

 the dimensions griven in the following: table :• — - 



A criticism of this procedure is given on page 72. 



Pleomorphism of Beggiatoa alba. 



Zopf (l) has found this organism to be highly pleomorphic: 

 it can exist in a motile free state, or in a non-motile attached 

 form. The long threads show a differentiation of base and 

 apex. 



The filament breaks up under certain conditions and forms 

 a mass of cocci. f In Fig. ja is shown a filament which has 



* The name Beggiatoa minima has been apphed to two different organisms, 

 this name being given by Winogradsky to one organism, and hy Warming 

 to another. That described by Warming has since been taken away from 

 the Bacteria by Lauterborn, and placed in another group under the name 

 Spirophis minima. 



t Zopf uses the term coccus, not to designate an individual belonging 

 to the group CoccacecB, but to indicate a small rounded mass of plasma. 

 In the accepted use of this term nowadays, a coccus is a spherical mass of 

 plasma surrounded by a definite cell membrane. 



7* 



