36 Lectures on Bacteria. [§ iv. 



position in the organic world and their natural affinity to other orga- 

 nisms. The question is of only secondary interest to us on the 

 present occasion, and must not therefore be examined at any length. 



If we compare the structure and development of Bacteria with 

 those of other known creatures, as we must do to answer the 

 above question, the arthrosporous Bacteria are seen to agree 

 entirely in all essential points with the members of the plant- 

 group of Nostocaceae in the wider sense of the word; only 

 the Nostocaceae are furnished with chlorophyll in conjunction 

 with another blue or violet colouring matter which is soluble 

 in water, and are thus distinguished from the Bacteria which 

 contain no chlorophyll. There is no reason why the arthro- 

 sporous Bacteria should not be termed Nostocaceae which 

 are devoid of chlorophyll. Structure, growth, occasional for- 

 mation of Zoogloeae, more or less constant motility, especially 

 developed in the Oscillatorieae, a division of the Nostoca- 

 ceae, are the same in the two groups, so that apart from the 

 absence of chlorophyll there is no greater difference between 

 them than between the separate species of either of the groups. 

 This may be illustrated by the case of Leuconostoc described 

 on page 22. The name indicates that the plant entirely re- 

 sembles in all respects the bluish-green species of the genus 

 Nostoc which live in water and on moist sdl, only it is colour- 

 less and white. To this may be added, that most of the 

 Nostocaceae attain to considerably larger dimensions than the 

 Bacteria in their cells and in the aggregations of their cells, and 

 that the members of the group which resemble the Bacteria are 

 related to other forms of a more varied and higher differentia- 

 tion and conformation. 



The Bacteria which we have distinguished as endosporous 

 entirely resemble the arthrosporous Bacteria in every respect ex- 

 cept the peculiar formation of spores, and resemble no other 

 known organisms. We must therefore place them next to the 

 arthrosporous division, at least for the present and in accord- 

 ance with our present knowledge. 



