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HORTICULTURE FOR SCHOOLS 



portion of the plant, and here the bacteria that produce the 

 disease grow and multiply with amazing rapidity. From the 

 tips of the branches they spread downward, killing the limb 



as they advance. The leaves are 

 left without nourishment and very 

 soon wilt and die, making the limb 

 appear as if it had been injured by 

 too much heat. On this account, 

 the disease is sometimes called fire- 

 blight. If the bacteria gain access 

 through a small branch which grows 

 on one of the larger limbs, the 

 disease may entirely encircle and 

 kill it; or if they gain access 

 through suckers that grow at the 

 base of the tree, they may kill the 

 FIG. 127. Pear-blight A diseased entire tree in a similar way in a 



twig; B, healthy twig. yery short i[mQ 



It has been demonstrated that insects flying from flower 

 to flower are chiefly instrumental in spreading the disease. 

 Bees are probably the chief agencies in this respect. These 

 come in contact with the disease on one plant or part and 

 then carry the bacteria with them when they fly to other 

 unaffected portions. 



A limb or other part of the tree that has been attacked 

 cannot be cured. The bacteria are located under the bark 

 where they cannot be reached by any spray and are not sub- 

 ject to surface control. It has been necessary, therefore, to 

 devise other means of treatment, such as amputation of the 

 diseased parts. Wherever wilting appears, indicating the 

 presence of disease, the limb should be cut off immediately. 

 To avoid any possible infection, the scissors or pruning- 

 shears with which the cut has been made should then be 

 dipped in corrosive sublimate 1 solution prepared one to one 

 thousand. The wound should be disinfected with a solution 



