Dale . — A Bacterial Disease of Potato Leaves . 151 
generally be too thick, and the temperature too high, to allow of the 
penetration of the organism. Any considerable attack would, however, be 
serious, as the leaves and shoots are completely destroyed and the forma- 
tion of tubers consequently stopped. The disease has been most marked in 
plants grown in a cool greenhouse. The organism causing the disease is 
a bacillus differing in so many respects from those previously described as 
the cause of other potato diseases that it must be considered as a new 
species. On account of its power of forming infection tubes in the host 
plant it has been named Bacillus Tubifex , n. sp. 
In culture it forms slimy masses of zoogloea on steamed potato tuber. 
These masses string out and stretch in films over large bubbles of gas, 
which are given off as the organism grows. The Bacteria have the power 
of causing fermentation. They are aerobic and anaerobic, and can live 
either as parasites or as saprophytes. Spore formation readily occurs. 
My grateful thanks are due to Professor Biffen for allowing me to work 
in the School of Agriculture and at the University Farm, and for helping 
me with his advice during the course of my investigations. 
Table showing the Characteristics of different Bacteria 
PATHOGENIC TO SOLANUM TUBEROSUM. 
1. 
2. 
3 - 
4 - 
7 - 
8 . 
9 - 
10. 
Bacillus Solanacearum 
(Smith). 
Not sticky in the plant or 
on culture media, except 
slightly on agar. 
Dirty white or yellowish 
white, then brownish and 
finally smoke-black. Browns 
vascular bundles. 
Strictly aerobic. Will not 
grow in closed fermentation 
tubes with any sugar. 
No acids with any sugar. 
Intense alkali, producer. 
Slowly saponifies milk. 
Decided but not particularly 
obnoxious smell — like som e , 
but not all, rotting potatoes. 
Grows readily at 37 0 C. 
Thermal death-point 52°C. 
Zoogloea in top layers of 
beef broth or peptone water 
as innumerable tiny whitish 
flecks, which are sometimes 
slightly inclined to unite 
into pellicle but diffuse 
through the liquid on shak- 
ing. 
Bacillus melanogenes 
(Pethybridge). 
Exceedingly sticky and slimy 
in cultures, especially on 
potato tuber. It strings out 
from the needle. 
White, except on sterile 
potato. 
Slight growth occurs in stab 
cultures covered with agar. 
Forms acid in glucose broth 
and in cane-sugar broth. 
Coagulates milk within 48 
hours. Gas bubbles formed. 
Colour of litmus goes. 
Thermal death-point between 
45 0 and so°C. 
Zoogloea not recorded. 
Bacillus Tubifex , n. sp. 
Like B. melanogenes , 
White, then dirty white. 
Not strictly aerobic. Will 
grow in presence of caustic 
soda and pyrogallin, and 
also in agar stab covered 
with agar. 
Forms acid in cane-sugar and 
peptone in gelatine. 
Coagulates milk in 1 or 2 
days with formation of acid. 
Gas bubbles formed. De- 
colorizes neutral litmus. 
Slight odour. On living 
potato smells ammoniacal. 
Grows readily at 35° C. 
Thermal death-point between 
45 0 and 50° C. 
Like B . Solanacearum , but 
also forms films on the sur- 
face which break up and 
sink when the fluid is shaken. 
