528 Bacteria as a Cause of Disease in Plants. [July, 
ecuted until June, 1880, when the unusual prevalence of the dis- 
ease called more special attention to it. The same organisms, or 
those very similar, were as uniformly found in the tissues of apple 
trees suffering with the disease called twig blight. On diseased 
parts of both trees, drops of whitish, viscid material were often 
found, oozing from the bark, and this proved to be almost wholly 
made up of the bacteria. After some hours’ exposure the mass 
became yellowish, and finally dark-brown. These bacteria are 
generally double jointed, each article being about .oO1 mm. 
(.0000393 in.) in transverse diameter, and about .oo15 mm. long. 
Sometimes, however, the oval single forms are common, and not 
unfrequently lonyer ones of several joints are found. 
Upon examining the infected tissues, the absence of the starch 
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Diseased Pear Bark, from limb three weeks afer blight commenced. Magnified 
granules, so abundant in the healthy cells, was especially marked. 
Tests revealed the fermentation of this starch with the evolution 
of carbon dioxide, hydrogen and butyric acid. The other car- 
bonaceous materials in the cells, as sugar, malic acid, &c., doubt- 
less undergoes the same fermentation, but being soluble in water 
their loss is not rendered evident by the microscope. The ce 
walls contrary to my expectation, were not found injured, neither 
was the protoplasm involved in the fermentation. i 
By passing a thin section of the bark under the microscopes it 
is possible to find in the same slice, all variations, from perfectly 
healthy cells to those which have lost the whole of the store® 
starch, the bacteria likewise varying in numbers as the destruc 
