Dale . — A Bacterial Disease of Potato Leaves . 147 
Several series of sections through the edges of leaves showed Bacteria 
entering between the cells and not by the stomata. 
%. Material infected in 1911. The open-air experiments in 1911, in 
the earlier part of the season, gave more positive results, though on account 
of the hot, dry weather, these were fewer than had been hoped and expected. 
Of the plants infected on June 8 some leaves were cut and examined fresh 
on June 23, i. e. fifteen days after infection. As before stated, it is difficult, 
except in the larger veins, to see tubes in fresh material on account of the 
presence of chlorophyll. It is quite possible, therefore, that tubes in the 
lamina may have been overlooked. 
Three leaflets from a plant of ‘ White City ’ infected with the original 
organism were cut. The signs of disease were not far advanced, and the 
leaflets were only slightly brown. A very definite tide was seen in the first 
leaflet cut. From these leaflets a fresh culture of the organism was made, 
which resembled the original culture. On June 30, that is, twenty-two 
days after infection, some more leaves were cut. A leaf of £ Up-to-Date ’ 
infected with the original organism contained good tubes in a vein which 
was cut. One large tube and some smaller ones were also seen in a leaf 
from a plant of ‘White City’ infected with the original organism (Fig. 20). 
A leaf of ‘ White City ’ infected with the thick gelatinous form also con- 
tained well-marked infection tubes and also many fungal hyphae. There is, 
however, no danger of confusing the two, as the fungal hyphae are thin- 
walled, have granular contents, branch, and are septate, whereas the bacterial 
tubes have thick refractive walls, and a narrow* lumen with no contents, and 
seldom branch. There is, however, a doubt as to whether these tubes were 
really formed by the gelatinous organism or by the original Bacteria, as the 
infections were made on the upper side only, while the tubes were found 
only on the lower side. It is possible that some of the original Bacteria, 
known to form tubes, may have been transferred from one plant to another 
by the hands of the operator. To avoid this danger, subsequently only one 
kind of organism was used for infection on a given day, as there were no 
means of sterilizing one’s hands properly in the field. 
After this time, however, a severe drought set in, and the plants also 
became attacked by Cladosporium. No definite and unmistakable tubes 
were found in the leaves which were subsequently cut, except on July 8, 
on another leaf of ‘White City’ infected on June 8 with the original 
organism. It is noteworthy that the tubes were confined to the upper side 
of the leaf, and that the upper side only had been infected. The leaf was so 
very slightly diseased that to the naked eye it seemed almost healthy. 
No tubes were found in plants infected with the organism which was 
obtained from the plant in 1911, and which seemed identical with that 
obtained in 1910. Bacteria were, however, found inside infected leaves. 
Leaves infected with the gelatinous organism, though showing no tubes, 
