THE PRINCIPLES OF CLASSIFICATION 87 



Key to the Chroniatiecs : 



Genus i. Chroniatium. — Cells motile, with polar cilia 



and cylindrical. 

 Genus 2. Rhabdomonas. — Same as preceding, only cells 



have a tendency to a spindle shape. 

 Genus 3. Thiospirillum. — Same as above, only cells are 



spiral. 

 Genus 4. Rhodocapsa. — Cells spherical, or nearly so, 



and non-motile, not capsulatcd. 

 Genus 5. Rhodothece. — Same as preceding, only cells 



capsulated, and in pairs. 



Remarks on Buchanan's Scheme of Classification. 



In the above scheme only that part which deals with the 

 sulphur bacteria is here considered. All the niemxbers of this 

 group are included in the order Thiohacteriales, which is one 

 of the six into which the Schizomycetes are divided. There are 

 twenty-two genera in this order, but no new species of sulphur 

 bacteria. 



The different genera of the sulphur bacteria arc all included 

 in the one order. It is evident that the classification of the 

 sulphur bacteria has been drawn up without specific investiga- 

 tion of these organisms, and without discrimination between 

 the values of various attributes. The characters chosen for 

 effecting the grouping are merely mixtures of the characters 

 used in previous classifications. The result is naturally the 

 perpetuation of all the errors that are found in the previous 

 schemes. Whilst Buchanan's scheme appears to be more 

 complete than older classifications, it is nof, so far as the 

 sulphur bacteria are concerned, and in essentials is no advance 

 on Winogradsky's plan. 



In the scheme drawn up under the aegis of the American 

 Society of Bacteriologists, the grouping of the sulphur bacteria 

 follows very closely the plan laid down by Buchanan. New 

 generic and specific names appear, but as these did not appear 

 as the result of independent investigations, the scheme is 

 cumbersome without compensating advantages. 



