No. 615] 



BACTERIAL PHYLOGEXY 



23o 



or true bacteria, are generally regarded as the least 

 specialized and possibly the most primitive. It is pos- 

 sible that tlie great group of the sulphur bacteria, the 

 order Thiobacteriales, is equally primitive, though the 

 genera and species have been less studied and are not a- 

 well known. There are unquestionably many iutergrad- 

 iim forms between the K n In >et e r iaics and the Thiobacteri- 

 ales, as shown by close parallel series of morphological 

 types. It seems equally clear that there are intergrading 

 forms between the Thiobacteriales and the blue-green 

 alga?. Morphologically, too, one may find every grada- 

 tion between the typical colorless, sulphur-containing 

 Beggiatoa, through species of this genus showing bac- 

 teriopurpurin. through the faintly colored, slender Oseil- 

 latoria to the thick, deeply pigmented forms. If these 

 intergradations and indicated relationships are real, it is 

 apparent that the true bacteria may have come from the 

 bine-green alga? through the sulphur form-, or the blue- 

 greens may have come from the true bacteria, or the 

 sulphur forms may be closer than either of the other 

 groups to the primitive types from which all three groups 

 have been derived. While there is no definite proof ap- 

 parently possible at the present time, it is not at all im- 

 probable that the last assumption is the true one. A 

 relationship quite certainly exists between the group of 

 sheathed filamentous bacteria (the Chlamydobacteriales) 

 and the blue-green algffi. The resemblance is so well 

 marked that certain species of the iron bacteria are quite 

 commonly included by algologists among the algae. The 

 relationship to the Eubacteriales is not quite so clear. 

 Possibly the genus Spharotilus {Cladothrix) may be re- 

 garded as a link, for this organism consists of rod-shaped 

 cells occurring in chains, all embedded in a gelatinous 

 sheath. Motile cells (gonidia) with polar flagella some- 

 what resembling Pseurlomonas types may be developed. 



The fungi apparently are related to certain of the bac- 

 teria through the Actinomycetales. This latter group 

 has some resemblance to certain of the true bacteria such 



