Jan. 15, 1917 
Blackleg Disease of Potato 
103 
DETAILS OF COMPARATIVE STUDIES 
MORPHOLOGY 
B. atrosepticus , B. solanisaprus, B. melanogenes , and the three organ¬ 
isms studied which were isolated from Maine potato stems were found 
to agree in all essential morphological characters except for certain vari¬ 
ations in size. They are motile, rod-shaped organisms with peritrichiate 
flagella, approximately three times as long as broad, occurring singly 
and in pairs, and in unstained preparations from young cultures often 
showing chains of several individuals. Frequently, however, rather 
thick rods with very little difference in the two dimensions were observed, 
more especially in preparations made from the decayed tissues of inocu¬ 
lated tubers. The organism obtained from Dr. Appel as B . phytoph- 
thorus , while agreeing in other morphological characters, was distinctly 
smaller in size and the ratio between length and width was decidedly 
less. No evidence of spore formation was obtained. Involution forms 
were not observed, although Harrison (17) reports them for B. solani¬ 
saprus when grown at 37 0 C. In this connection it may be mentioned, 
as is stated later, that at this temperature the writer has been unable to 
secure visible growth of any of the pathogenic strains either on agar 
slants or in tubes of beef broth. 
For making measurements all of the different strains studied, except 
that obtained from Dr. Schuster as B. phytophthorus (which was a non- 
pathogenic organism plainly of an entirely different type), were stained 
with aqueous gentian violet, anilin water gentian violet, aqueous methy¬ 
lene blue, alkaline methylene blue, aqueous fuchsin, and carbol fuchsin. 
These preparations were made from agar slants 36 to 48 hours old. 
Flagella were stained by a modification of the Pitfield method. 1 
The results of these measurements are given in tabular form below. 
Table I gives for each organism the extremes in length and breadth and 
the average size obtained as shown by all the stains collectively. The 
second presents the same data for each organism for each separate stain 
used. 
Table I .—Extreme and average measurements {in microns) of each organism as obtained 
from using six different stains 
Organism. 
B. atrosepticus ... 
B . solanisaprus . 
B . melanogenes .. 
IIIA. 
SE. 
IIP. 
B . phytophthorus from Appel 
Width. 
Length. 
Average size. 
0. 4 to O. 8 
I. 3 to 2. 5 
0. 5 by 1. 8 
.4 to .7 
I. O tO 2. 2 
• 5 by 1. 4 
. 4 to .8 
I. 2 tO 2 . 4 
• 5 by 1. 7 
. 5 to I. I 
1. 3 to 3 - 3 
. 7 by 2 
. 4 to .8 
1. 3 to 2. 5 
. 6 by 2 
. 4 to .8 
i. 3 to 2. 9 
.6 by 1. 9' 
•3 to .7 
. 5 to 1. 6 
•5 by .9 
1 The writer wishes to acknowledge the aid rendered by Messrs. M. Shapovalov and A. Strauss in assist- 
ingin making many of these preparations, particularly the laborious task performed by the latter in making 
the large number of measurements of stained organisms, which is the basis of the data here presented. 
