THE PRINCIPLES OF CLASSIFICATION 8i 



1. Cells contain free sulphur. 

 Family (i) Thiorhodacece. 



[a) Cells united into families. 



Sub-family a. Thiocapsacece. — Division of cells in 



three directions of space. 

 Sub-family h. LamprocystacecE. — Division of cells 



first in three, then in two directions of space. 

 Sub-family c. Thiopediacece. — Division of cells in two 



directions of space. 

 Sub-family d. Amcehobacteriacece. — Division of cells in 



one direction of space. 

 ib) Cells always swarming. 



Sub-family^. ChromatiacecE. — Not capsulated. 

 Sub-family /. Rhodocapsacece. — Capsulated. 



2. Cells do not contain free sulphur. 

 Family (2) Athiorhodacecs. 



[a) Cells united into families. 



Genus a. Rhodocystis. — Cells rod-shaped, many being 

 embedded together in a common capsule. 



Genus b. Rhodonostoc. — Cells spherical or short rods 

 in chains, each chain enclosed in a capsule. 



[b] Cells free. 



Genus a. Rhodococcus. — Cells spherical, non-motile. 

 Genus b. Rhodobacterium. — Cells straight rods and 



non-motile. 

 Genus c. Rhodobacillus. — Cells, motile rods. 

 Genus d. Rhodovibrio. — Cells, short, bean, or comma 



shaped ; monotrichous, actively motile. 

 Genus e. Rho do spirillum. —Cells, spiral ; actively 



motile ; polar ciliation. 



Remarks on Molisch's Classification. 



Molisch did not investigate the colourless sulphur bac- 

 teria, and in the present work we are not dealing specifically 



with the sulphurless purple bacteria. His classification has 



6 



