149 
Dale.— A Bacterial Disease of Potato Leaves . 
and tubers, whereas in the disease here described the mischief not only 
begins in the leaves but is exclusively confined to them, so that, as far as 
can be determined at present, the stems and tubers are only indirectly 
affected by means of the destruction of the foliage. As is to be expected, 
the organisms isolated in each case also differ from one another. In the 
potato bacteriosis y described by Erwin Smith ( 1 . c.), the parts, chiefly attacked 
are also the stems and tubers, though the organs first attacked are the 
leaves, as in the disease now being described. But the two diseases differ 
essentially in the fact that, while in bacteriosis the vascular tissue is first 
attacked and the vessels blocked with the organism, the parenchyma being 
only affected subsequently, in the present disease the injury begins in the 
parenchymay and spreads to the non-vascular tissues of the veins, while not 
apparently affecting directly the stems and tubers. For convenience in 
description the latter disease may shortly be called bacterial leaf disease to 
distinguish it from bacterial diseases chiefly affecting other organs, and also 
to distinguish it from leaf diseases, such as 4 blight ’, due to Phytophthora or 
other Fungi. The mode of infection in the two diseases is also different. 
B. Solanacearum enters the vessels by means of the water stomata or through 
wounds, whereas in bacterial leaf disease the organism pierces the uninjured 
epidermis and passes first between the cell-walls. 
Again, as might be expected, there are marked differences between the 
organisms causing the two diseases. The differences between the three 
organisms, viz. B. Solanacearum y causing bacteriosis, B. melanogenes , causing 
black stalk-rot, and the bacillus causing bacterial leaf disease, may most 
readily be seen and compared by means of the accompanying table 1 (p. 1 5 1 ). 
There seems to be no doubt, as a study of the table shows, that 
the organism causing bacterial leaf disease differs markedly from those 
already described, and that it must therefore be regarded as a new species, 
reluctant though one is to add another to the already long list. Since its 
most distinguishing characteristic is the power of forming tubes in the 
tissues of the host, like those already known in the Leguminosae, the 
most obvious specific name is one indicating this character. I propose, 
therefore, to call it B. TubifeXy n. sp. 
The species, though parasitic on potato leaves, is also a saprophyte, as it 
grows strongly on various culture media as well as on the living leaf and tuber. 
With regard to the mode of formation of the tubes a few words may 
here be said. 
The organism evidently pierces the epidermis and passes between the 
cells by a process of fermentation in which the middle lamella is dissolved. 
That Bacteria possess this power h,as already been demonstrated by previous 
1 Reference may also be made to the table given by Erwin Smith, in the paper above referred 
to, showing the differences between B. Solanacearumy B. tracheiphilus (the organism causing 
cucumber rot), and ‘ Kramer’s Bacillus causing a rot in potato tubers. 
