90 SUMMARY OF CURRENT RESEARCHES RELATING TO 



place beyond doubt the affinity of the new organism, which Van 

 Tieghem calls Bacterium viride. 



In May and June the author again observed, in water containing 

 aquatic plants mingled with Sjnrogyra, very slender filaments of a 

 green colour verging on yellow, ordinarily immotile, but sometimes 

 endowed with motion, formed of long cells, and bearing a close 

 resemblance to Bacillus anthracis. In September he was able to 

 follow the formation and the germination of the spores. These were 

 oval in form, and were abundantly produced in all the cells of 

 filaments placed for some days in darkness. They were completely 

 colourless. On germinating they gave rise to filaments, which were 

 at first colourless but which rapidly became green on exposure to light. 

 This organism, possibly identical with Hi/pheGthrix or Leptothrix 

 tenuissima, is apparently common, and is called by Van Tieghem 

 Bacillus virens. The same or a very similar form was described by 

 Perty under the name Sporonema gracile, in which the formation of the 

 spores was described and drawn by him. 



2. Colourless Phycochromacece. — Two genera have been formed of 

 PhycochromacesB destitute of chlorophyll — one, Beggiatoa, with the 

 ordinary motion of an Oscillatoria ; the other, Leptothrix, immotile. 

 A third form has been studied by Van Tieghem, with colourless, 

 extremely slender, immotile filaments, composed of short cells. It is 

 especially characterized by nodosities in the filament, consisting of 

 permanent cells more refrangent than the rest, which germinate after 

 the rest have disappeared. From this circumstance the author regards 

 it as a true Oscillatoria, which should not be separated from this 

 family and united to Leptothrix merely for the absence of motility. 

 Notwithstanding the absence of chlorophyll, and the outward resem- 

 blance to a Bacillus, there is not sufficient reason for separating this 

 organism from the section Beggiatoa of Oscillatoria, and Van 

 Tieghem proposes for it the name Beggiatoa nodosa. 



The same author has observed a Spirulina entirely destitute of 

 chlorophyll forming a thin white layer in an abandoned mill-race. It 

 was extremely slender, and its coils so close together as to touch, and 

 to appear to form a hollow tube. It moved actively by torsion on 

 the axis of the tube ; and the very long filaments oscillated at the 

 same time laterally. Van Tieghem calls it Spirulina alba, and 

 considers it nearly allied to *S^. subtilissima. 



3. Affinity of Bacteriacece and Phycochromacece. — It appears, there- 

 fore, that (1) normal chlorophyll occurs in types belonging certainly 

 to the family Bacteriacefe, and not separable generically from 

 Bacterium and Bacillus ; (2) various Oscillatoriefe are altogether 

 wanting in the blue-green colouring matter ; and (3) permanent cells 

 have been observed for the first time in a Beggiatoa. Van Tieghem 

 does not, from these facts, draw the conclusions that the distinction 

 between the two families must be abandoned, as was proposed by Cohn 

 in 1875. In the occasional loss of their chlorophyll the Oscillatoriete 

 do not, in fact, aj^proach the Bacteriacefe ; and, in occasionally 

 acquiring chlorophyll, the Bacteriaceaj do not approach the Oscilla- 

 torioae. The two chlorophylls aro not equivalent; that of the 



