134 Dale . — A Bacterial Disease of Potato Leaves. 
May 12, 1909. Besides these tubers, cuttings of shoots from apparently 
healthy tubers were planted. It is noteworthy that the plants grown from 
these cuttings were not attacked by the disease, which appeared on the 
plants grown from the * blind ’ tubers. 
Each of the three tubers produced shoots which at first were apparently 
healthy. But by June 10, i. e. in about a month after the tubers had been 
planted, the shoot of ‘ plant 3 5 began to show symptoms of disease. The 
leaves were somewhat wrinkled, becoming slightly yellow and covered with 
small brownish spots. 
One of the leaves was cut. In the fresh leaf the brown spots were seen 
to be due to isolated cells, or rows of cells, densely filled with granules 
showing active movement. These cells are to be distinguished from other 
cells containing colourless crystalline granules. 
In the former cells the granules are stained by dyes, while in the latter 
the granules are not stained and are refractive, so that if the granules are 
examined in reflected light they appear white, whereas the stainable granules 
are black, though both usually exhibit active movements in sections of fresh 
leaves. The stainable { granules ’ were found later to be Bacteria. 
By June 15 ‘ plant 3 ’ showed clear symptoms of ‘ leaf-curl ’. The leaves 
were rolling up at the edges and were going yellow in large patches, and 
the veins of the leaves were turning brown from the edge towards the centre 
of the leaves. The leaves gradually became more yellow and dropped off, 
from below upwards. Sections of the leaves with brown veins showed that, 
in addition to the isolated cells with stainable granular contents, referred to 
above, the vascular tissues were turning a bright brown. At this stage were 
first observed, in the larger veins, certain colourless tubes, with highly refrac* 
five walls, of very irregular size and thickness. These tubes were obviously 
not fungal, and their significance and nature were not at first apparent. 
In ‘ plants 1 a and 1 b ’ there were similar signs of disease, and sections 
showed both cells with granules and also large numbers of tubes. 
By June 21 ‘ plant 1 a ’ (which had been covered with a bell-glass for 
about a week) was almost dead. It had five large shoots (one had been 
cut off and fixed earlier) and three small shoots. Three out of the five had 
no green leaves ; the stems were yellow and covered with elongated brown 
patches. The leaves were brown, shrivelled, and very slightly attached to 
the stem. The other two shoots had green stems with a few yellowish 
green leaves at the top. The three short shoots had yellowish green or 
brown leaves. 
‘ Plant x b\ which had not been covered, had green leaves on all its 
three shoots, but the veins were going a purple-brown colour on the under 
sides of the leaves, and the leaves were shrivelling from the tips downwards, 
while some were dropping off. c Plant 3 ’ was almost as badly affected as 
4 plant 1 a\ 
