304 THE PARASITIC DISEASES OF PLANTS. 
The Bacterioses and Rots. A single illustration of this 
type must suffice. 
The Fire Blight of the pear, quince, apple, etc., (B. amylovorus .) 
This bacterium attacks various members of the apple family anc 
a number of other plants as well. The disease has been knowr 
for over a century and almost every conceivable explanation has 
been given for it. That it is caused by a bacterium has been finalh 
demonstrated by the isolation of the organism and the reproductior 
of the disease by inoculation experiments. In the form known a: 
the twig gall, the first indication of the disease is commonly seen in i 
browning or blackening of the leaves of the young shoots, which soor 
die. It then extends into the stem by the way of the inner bark, causing 
it to become blackened. The whole of this tissue is destroyed by the 
bacterium, causing a 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 o: 
winter, it remains alive in the stem till warm weather, when it onc( 
more begins its work of destruction. In moist weather a viscic 
mass extends from the canker spots, containing bacteria. Littk 
is known of its means of distribution, although it is thought tha 
it may find entrance through the flowers and be carried to them b} 
bees. 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 taker 
to be thorough in the pruning and to cut away every bit of diseasec 
wood. 
Other examples of this type of bacterial diseases are the following 
Bean blight, produced by Bact. Phaseoli. 
Cotton bacteriosis, produced by Bact. malveacarum. 
Walnut bacteriosis, produced by Pseud, juglandis. 
Mulberry blight, produced by B. cubonianus. 
Black spot of plum, produced by Pseud. Pruni. 
Wakker's disease of hyacinth, produced by Bact. Hyacinthi. 
