THE PEAR BLIGHT 45 



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germs can also gain access through the tips of growing 

 branches where the green growth is soft and succulent, 

 and, no doubt, they occasionally enter throus-h cracks 

 in the bark. 



After the bacteria haye gained access to the tissues 

 •of the tree they multiply rapidly, and generally in the 

 course of a few weeks haye become so abundant as to 

 show their presence by blackeuiug the bark or blossoms. 

 ^'As the disease progresses," says Professor Arthur, 

 *Hhe germs exude on the surface, and the gummy sub- 

 stance thus produced is washed olf ; the gum is dissolyed 

 and the germs set free and washed into the ground. 

 The germs multiply there in rich mold and grow all 

 winter, or year after year. In a dry time the wind takes 

 up the germs into the air, or they may be taken up by 

 simple evaporation. Now when the surface of the tis- 

 sues is tender and moist, as in spring, the air, laden 

 with these germs, playing oyer the trees, brings the 

 germs in contact with the delicate tissues. The germs 

 are held there by the moisture and enabled to grow ; the 

 disease gets a foothold, and in the course of a month or 

 two it shows itself by the sudden blackening of the 

 leayes." Insects also carry the germs to blossoms. 



Treatment. — No successful method of preyenting 

 the disease by artificial applications to the trees has yet 

 been found. But it has been shown that if the trees are 

 carefully watched during the season of growth, and the 

 affected twigs cut off (at least a foot below the lowest 

 point of injury) and burned, the damage done may be 

 greatly lessened. Professor Burrill advises the examina- 

 tion of the trees once a fortnight, and states that the 

 bark reveals the damage best after a shower, when the 

 surface is wet. It is important, also, to keep the bark 

 free from wounds. 



The fact that slow growing pear trees are less liable 

 to injury by blight than those of rapid growth has long 



