SCHIZOMYCETES. BACTERIA 123 



Host plants. This species has received the name of pear blight 

 on account of the fact that it is a more disastrous and more com- 

 mon disease upon the pear {Pyrus communis) than upon any other 

 of its numerous hosts. It is also found as a parasite of the 

 apple {Pyrus Malus), quince (Cydonia vulgaris), and of numerous 

 species of native pomaceous plants, such as wild crabs (Pyrus) 

 and hawthorn (Crataegus), and recently it has been found on the 

 plum. There is considerable difference in the susceptibility of 

 the various varieties of pears. The growing of Bartlett and 

 many other desirable varieties of our common pears in the south- 

 ern states and in the Mississippi Valley has been very largely 

 given up on account of the destructiveness of this disease. Such 

 varieties as the Bartlett, Seckel, and Le Conte are much more 

 susceptible, at least in most sections of the country, than such 

 as the Kieffer, Duchess, and Winter Nelis. The Oriental group 

 in general is more resistant, although the several varieties are by 

 no means free from the disease under conditions favorable for its 

 development and propagation. 



The pear blight is also a serious disease on apples, and there 

 seems to be less difference in resistance among these fruits ; 

 nearly all of the standard varieties being more or less affected. 



Symptoms. The pear blight is more commonly noticed during 

 the early part of the season, when it appears in the form of twig 

 blight throughout the blossoming period of both pears and apples. 

 From two weeks to one month after the period of pollination the 

 blossoms and tips may begin to wilt and show signs of general 

 blackening, resulting finally in the complete blackening and death 

 of all branches or spurs upon which flower clusters have been 

 borne. In some instances scarcely a flower tip upon an infested 

 tree is free from this general attack. As a matter of fact, the in- 

 fection usually takes place at the time of blossoming and the dis- 

 ease is most abundantly distributed at that time, as will be shown 

 later. Upon the pear the blight may continue to extend down the 

 twig or the branch, the branch being entirely killed as it progresses ; 

 and in the course of some months it may have extended into the 

 larger limbs, or into the main body of the tree (Fig. 31). Water 

 shoots may also be affected both in the case of the pear and the 

 apple (Fig. 32), and direct entrance to the body gained after a 



