ASCOMYCETES 



267 



There are probably no varieties of the pear or apple which 

 are entirely free from scab. Nevertheless, there is a great dif- 

 ference in susceptibility. In New York, Flemish Beauty, Sum- 

 mer Doyenne, Duchess, Clairgeau, Sheldon, Seckel, Anjou, and 

 Lawrence have been reported as more generally affected than 

 Le Conte, Kieffer, and Bartlett. In California the later varieties 

 like Winter Nellis and Easter Beurre are said to be more sus- 

 ceptible than the Bartlett, which, however, is only resistant to 

 an intermediate degree. The susceptibility of different varieties 

 of apple to the apple scab seems to vary considerably according 



FIG. 119. CONIDIAL STAGE: FUSICLADIUM OF THE PEAR SCAB FUNGUS 



to the region in which grown, yet nearly all of the standard 

 varieties may be affected during seasons favorable to the fungus. 

 The fungus. The spores of the Fusicladium stage germinate 

 readily in water and develop a short germ tube, or sometimes 

 two germ tubes. The germ tube sometimes forms a dark spore- 

 like structure, if the conditions are not favorable for further rapid 

 growth. This structure is scarcely in the nature of an appres- 

 sorium, and may be considered a resting stage, which will grow 

 out into mycelium under favorable conditions. It is believed that 

 the mycelium of these two species of fungi develops for a short 

 time superficially, then penetrates the epidermis in some way. 

 At any rate, the mycelium is found at a very early stage beneath 



