THE PRINCIPLES OF CLASSIFICATION 83 



Buchanan's Classification (1917). 



He distinguishes six orders of the class Schizomycetes. 



Order i. — Enhacteriales. 

 Order 2. — Chlamydohacteriales . 

 Order 3. — Actinomycetales. 

 Order 4. — Thiobacteriales. 

 Order 5. — Myxobacteriales. 

 Order 6. — Spirochcetales. 



He gives the following key to the families of the order 

 Thiobacteriales, which includes all the sulphur bacteria. 



Family (i) Achromatiacece. — With sulphur, but no pur- 

 purin. 

 Unicellular : not motile, and not filamentous. 

 Genus i. Achromatiiim. — Cells ellipsoidal, containing 



calcium oxalate, and perhaps sulphur. 

 Genus 2. Thiophysa. — Spherical cells, with sulphur 



granules in a central vacuole. 

 Genus 3. Hillhoiisia. — Cells longer, and very large 

 (42 — 86/a), with peritrichous cilia. 



Family (2) Beggiatoacece. — Like family (i), but filamentous. 



Genus I. Thiothrix. — Non-motile filaments, thread un- 

 equally thick ; attached. 



Genus 2. 5^^^w/oa.— Filaments, motile, not attached, 

 thread cylindrical ; filaments not in bundles, nor 

 surrounded by a gelatinous sheath. 



Genus 3. Thioploca. — As Genus 2, but filaments in 

 bundles surrounded by a gelatinous sheath. 



Family (3) RJwdobacteriacece. — Containing bacteriopur- 

 purin, and with or without sulphur granules. These he divides 

 into two sub-families : — 



Chromatioidece. — Containing sulphur granules. 

 Rhodobacterioidece. — Without sulphur granules. 



Chromatioidece. — Divided into five tribes as follows : — 



ThiocapsecE. — Cells in families : division in three 

 directions of space. 



