The Life-history of Bacillus hirtus. 
(Synonyms Bacterium hirtum, Henrici ; Pseudomonas hirtum, Ellis.) 
BY 
DAVID ELLIS, D.Sc., Ph.D. 
Lecturer in Botany and Bacteriology , Glasgow and West of Scotland, Technical College, Glasgow. 
With Plate XVI. 
Introduction. 
HIS investigation was commenced on the assumption that Bacillus 
A hirtus belonged to the genus Pseudomonas , because in a former work 
which I published (1) I found that the ciliation was polar (vide Migula’s 
classification, 11 , p. 46 ). Since then, however, I found that under cultiva- 
tion, this species became more motile, and when fresh cilia preparations 
were made the ciliation became peritrich. This was somewhat disappoint- 
ing because, so far as I am aware, the life-history of the genus Pseudomonas , 
from spore-formation to spore-formation in the next generation, has not 
been completely investigated. I carried on the work, however, because the 
only other investigator of this species, Henrici (7), has not given us a full 
account of its characteristics, and its developmental history is entirely 
wanting. It was placed by him in the genus Bacterium under the name 
Bacterium hirtum , because it appeared to him to be perfectly immotile. 
But as the following results will show, its motility under cultivation is as 
great as that of any Bacillus , and as its cilia are arranged all round the cell, 
it belongs to the genus Bacillus. As in my earlier investigation of this 
species ( 1 ) cilia were found only at the poles, the question still remains 
unsolved as to whether under cultivation a cylindrical form of cell may not 
change its ciliation from polar, to peritrich. The increase in its motility 
may be caused by that very fact. I propose relegating the solution of this 
problem to a later investigation. It is important to consider this question 
for, if true, it would mean that the two genera Bacillus and Pseudomonas 
would have to be merged into one genus embracing all the forms at present 
classed under the two genera. I do not know of a single species at present 
classed under the genus Pseudomonas which has been so long cultivated 
and in which cilia preparations have been so extensively made, that it can 
be stated with certainty that its ciliation is polar. I have already shown 
(2) that non-motile cylindrical forms of Bacteria under cultivation become 
[Annals of Botany, Vol. XX. No. LXXIX. July. 1906.] 
R a 
