328 THE PARASITIC DISEASES OF PLANTS 
girdling of the tree. Then it extends down the stem, sometimes 
going at the rate of an inch a day, and eventually causing great 
injury or complete destruction. It particularly attacks the 
stored starch, converting it into a gummy substance. The 
diseased area may extend for a distance down the stem causing 
a, patch of “canker,” and if checked in its growth by the onset of 
winter, it remains alive in the stem till warm weather, when it 
once more begins its work of destruction. In moist weather a 
viscid mass extends from the canker spots, containing bacteria. 
It is carried to healthy plants by insects or by pruning tools that 
become contaminated in these drops of viscid exudate. It may, 
however, enter through wounds in the bark elsewhere. The 
only feasible method of fighting it of any value is to cut away the 
diseased parts as soon as the trouble appears, great care being 
taken to be thorough in the pruning and to cut away every bit 
of diseased wood. 
Other examples of this type of bacterial diseases are the 
following. 
Bean blight, produced by Bact. Phaseolt. 
Cotton bacteriosis, produced by Bact. malveacarum. 
Walnut bacteriosis, produced by Pseud. juglandts. 
Mulberry blight, produced by B. cubonianus. 
Black spot of plum, produced by Pseud. Prunt. 
Wakker’s disease of hyacinth, produced by Bact. Hyacinthi. 
Soft rot of carrots, etc., produced by B. carotovorus. 
Soft rot of sugar beet, produced by B. teutlium. 
Soft rot of stored celery, caused by Pseud. fluorescens. 
Rot of rts, produced by Pseud. iridis. 
White rot of turnip, produced by Pseud. destructans. 
Gummosis of beet, produced by B. Bete. 
Soft rot of ontons is also caused by bacteria, and there are some 
other diseases less well known. 
The Tubercular or Tumor Diseases. The Olive Knot (B. 
savastanot). ‘This disease, first studied in 1886, and attributed 
upon insufficient proof to a bacterial origin, has recently been 
