Thames Bacteria, III. 
BY 
H. MARSHALL WARD, D.Sc., F.R.S., F.L.S., 
Professor of Botany in the University of Cambridge . 
With Plates XII— XIV. 
I N previous papers I have given some types of Bacteria 
from the Thames, selected as showing very definite 
characters, some of which were studied in detail. During 
my investigations of the Thames Flora, however, it was con- 
stantly found that certain well-known types of Bacteria are 
represented by varietal forms of considerable interest because 
the close and continued study of them might be expected 
to throw light on the vexed questions of species and fixity 
of type in Schizomycetes. Some of these groups of varieties 
were studied for long periods, and the results of such work 
on one well-marked group are here offered. I regard the 
forms described below as all belonging to one type ; but 
since this breaks up very naturally into a series of yellow 
forms and one devoid of colouring-matter, it was judged 
convenient to regard them as forming two groups (VI and 
VII) in the survey given in the Fifth Report to the Water 
Research Committee of the Royal Society 1 . 
1 Proc. Roy. Soc., Vol. lxi, No. 376, 1897. 
[Annals of Botany, Vol. XIII. No. L. June, 1899.] 
