XV. 
BACTERIA OF PLANT DISEASES. 
I SHALL not attempt to give a full account of the bacteria which 
have been described as bearing an etiological relation to various in- 
fectious diseases of plants, but a “text-book of bacteriology” would 
be incomplete without some reference to the best known of these 
bacteria. In the following descriptions of species I have preferred 
to quote largely from the published papers of Dr. Erwin F. Smith, 
of the Department of Agriculturé, United States, a recognized au- 
thority in the investigation of plant diseases, rather than to rewrite 
his descriptions. 
BACILLUS SOLANACEARUM (Sinith). 
Causes a bacterial disease of the tomato, egg plant, and Irish 
potato. 
‘* Morphology.—A medium-sized bacillus, with rounded ends; often in 
pairs, with a plain constriction ; elliptical, but of variable size, depending on 
age of culture or the length of time the tissues of the plant have been occu- 
pied ; usually one and one-half to three times as long as broad. On cover- 
glass preparations made from peptone beef bouillon cultures forty-eight 
hours old and stained with a watery solution of methyl violet, many are 1.5 
by 0.5 x, but these measurements must not be taken too literally, since the size 
depends not only on the age of the culture but also on the kind of stain em- 
ployed, 7.e., on whether or not the cell wall stains. Organism motile, often 
only sluggishly so, especially when taken from the plant, but sometimes very 
actively motile, especially in young cultures. Flagella much longer than 
the rod; several—exact number and place of attachment not made out 
clearly, owing to imperfect preparations (Van Ermengem’s method), but ap- 
parently arising from any part of the rod. An attempt to stain them by 
Loéffler’s method was unsuccessful. No spores observed either in the plant 
or in culture media, but the search has not been continued long enough to 
warrant any opinion as to their existence. Zodgloea are formed almost from 
the start in fluid culture media. 
“ Symptoms Produced in the Plant.—The first indication of this disease, 
or at least the first one to attract the farmer’s attention, is the sudden wilting 
of the foliage. This may occur first on a single shoot, but finally it affects 
the whole plant. Subsequently, and especially if the plant is young or not 
very woody, the stem shrivels, first changing to a yellowish-green or to a 
muddy green, and finally to brown or black. The vascular bundles become 
brown long before the shrivelling takes place, and in the potato often show 
through the outer green parts of the stem as long, dark streaks, or the bac- 
teria run out on the petioles, after the manner of pear blight, forming nar- 
row, black lines. The vessels of such bundles are filled with the bacilli, 
