A Bacterial Disease of Potato Leaves, 
BY 
ELIZABETH DALE 
( Sometime Pfeiffer Student , Girton College , Cambridge ). 
With Plates XV and XVI. 
Contents. 
PAGE 
1. Symptoms and Mode of Occurrence 133 
2. Histological Characters of the affected Potato Plants . . .135 
3. The Parasitic Organism and its Culture 137 
4. Infection Experiments 143 
5. Examination of the artificially infected Plants . . . . . 145 
6. Discussion of Results 148 
7. Conclusions and Summary 150 
1. Symptoms and Mode of Occurrence. 
I N the course of some experiments made in 1909 with potato plants 
grown from tubers affected with ‘ blindness i. e. in which the ‘ eyes * 
had been more or less completely destroyed by Verticillium albo-atrum , 
certain pathological phenomena were observed which were at first thought 
to be due to the disease then under investigation, namely ‘ blindness \ 1 
Further observations, however, showed that two distinct diseases were 
in question. One of these, ‘ blindness affects the tubers and underground 
stems exclusively, while the other, which is due to Bacteria, is almost as 
exclusively confined to the leaves. 
The plants in which the latter disease was first observed were three, 
grown from tubers affected with ‘ blindness ’, and containing the mycelium 
of Verticillium albo-atrum. Two of these tubers had been kept in damp 
air for nine days, and had begun to form new and apparently healthy * eyes 
The plants grown from these tubers were labelled respectively ‘ 1 a * 
and ( 1 b\ A third tuber, which was dry and resting, had only traces of 
* eyes \ It was marked * 3 \ Each tuber was planted in a flower-pot on 
1 Dale : On the Cause of 1 Blindness ’ in Potato Tubers. Annals of Botany, vol. xxvi, No. ci, 
1912, p. 129. 
Annals of Botany, Vol. XXVI. No. CI. January, 191a.] 
