NOTE ON BACTERIUM IIUBESCENS. 281 



me iu this Journal^ vol. xiii, pi. xxiii. fig. 12, and after track- 

 ing it here and there over the field, have seen it arrested by 

 some obstacle, when a lashing movement can be most dis- 

 tinctly traced to a distance of thrice its own length behind 

 the plastid. I have never seen any indication of such a lash- 

 ing movement in front of the plastid. The presence of 

 highly refracting globules (loculi) in these large plastids en- 

 ables one most clearly to note the constant rotation of the 

 plastid on its own long axis. This frequently continues with 

 great activity for some seconds after locomotion has been 

 arrested. It is worth noting that the direction of linear 

 motion and of rotation is never permanently reversed in 

 these forms. 



In dividing specimens of Bacterium termo^ I have seen the 

 chain dart first in one direction, and then without turning 

 round return on its path with equal velocity. This can only 

 be due to the existence of a driving flagellum at each end of 

 the dividing chain. In the motile plastids of Bact. rubescens 

 I have 7iot seen this active reverse movement but only a 

 hesitating and feeble reverse movement, which soon gives way 

 to renewed rapid movement in the original direction. Pro- 

 bably Bact. rubescens is, like B. termo, amphiflagellate, but 

 has one (the younger formed at the pole of the last fission) 

 of its flagella much smaller than the other. Neither of 

 these flagella in any Schizophytae appear to be ' leading,^ but 

 always driving flagella. 



It does not appear to be necessary to have recourse to a 

 postflagellum to account for the movements of the remark- 

 able acicular plastids (figs. 28, 29, vol. xiii, pi. xxiii) which 

 I have found again in great quantity and beauty in speci- 

 mens of the crusts of Bacterium rubescens taken from the 

 surface of dead ivy-leaves at the bottom of a rain-water tank 

 in the Botanic Garden, Oxford. The slow serpentine 'crawl' 

 of the leptothrix-filaments of B. rubescens which I have fre 

 quently witnessed, is similar to that of Oscillarise and equally 

 difficult to explain. 



Dark granules supposed to be Sulphur by Professor Cohn. 

 The dark granules described by Professor Cohn in the motile 

 forms of Bacterium rubescens (his Monas vinosa, Okenii, &c.) 

 and figured by him as black specks (see his figures), are not 

 truly dark. What he has taken for darh granules are in 

 reality very bright, clear, highly refringent globules, which 

 I have spoken of in my previous papers as * loculi.' "When 

 the loculi are small they appear under feeble magnifying 

 power as black specks. These loculi appear to be a more 

 active part of the plastid differentiated from the surrounding 



