21 8 THE DISEASES OF FRUITS. 



met with upon apples, but it is more destructive to the cherry, 

 and will be considered with remedies under the latter fruit. 



There are several other diseases of the apple, as, for exam" 

 pie, some leaf-spot fungi, Phyllosticta ponecz Sacc., etc., that 

 injure the foliage, but the sprayings recommended will suffice 

 for them. 



THE PEAR. Fire Blight (Bacillus amylovorus Burl.). This 

 old, widespread, and dreaded disease in the pear orchard is 

 easily recognized by the brown dead leaves clinging to dying 

 branches, giving the appearance of having been scorched by 

 fire. Sometimes only a single branch or even a small twig is 

 blighted, and in other cases the whole tree may have been 

 destroyed, seemingly all at once or in a very short time. 

 This is one of the bacterial diseases and the fungus is very 

 different from any previously treated in this paper. Instead 

 of long slender filaments, as with ordinary fungi like mildews 

 and moulds, there are only exceedingly minute organisms that 

 multiply with great rapidity in the substance of the pear tree. 

 These germs winter over in the growing layer of the twig 

 and may ooze out through a rift in the bark along with the 

 juices of the stem. This exudation attracts insects ; by means 

 of these busy creatures the disease is carried to the opening 

 buds of the pear, and particularly the blossoms. The nectar 

 glands of the flower furnish a very acceptable food for these 

 verms, and in it they thrive and multiply with astonishing 

 rapidity, a single individual producing thousands in a few 

 hours. From the blossom the disease is carried to other 

 flowers and soon begins to spread down the twig from the 

 point of inoculation, the tender tissue and rich juices of the 

 shoot forming a suitable, well-protected place for the disease. 

 As it works its way down the stem, the line of march is along 

 the growing layer and protected from the outside world by the 

 overlying covering of bark. 



The amount of infection varies with the years and is some- 

 what dependent upon the weather. When, for example, 

 there are a rainy May and June there is apt to be an excess of 

 the blight. Fungi as a rule are favored by abundant moisture 

 and the bacteria are no exception to this rule. After the 

 germs are deeply seated in the older stems the amount of 

 rainfall may not have so much influence as the temperature. 



