184 SEVENTEENTH REPORT. 



Sitsceptibilitij of Varieties. Tlie \<ii'ieties of apples foniul to be 

 the most susceptible to this fiini»iis in Michijian are the Ciideou, 

 Wine Sap, Northern Spy, Ben Davis, and Jcmathan. It was ob- 

 served that aj)ples having an open calyx seemed more subject to 

 infection. 



It is rej)orted that the Kietter is the only variety «»f jicar suscept- 

 ible to attack by the disease. 



Syniptoins on the Apple. The fun<>us is conlined to the fruit, 

 the common \ntmt of infection being the blossom end. In the 

 case of infection through the calyx tube the disease is not notice- 

 able in its tirst stages unless the core is exposed, when the 

 typical dark hyphae are seen. This mycelial growth forms a gray 

 mass which covers the carpels and in many cases fills the entire core 

 cavity. In the later stages of infection, the frnit may become 

 entirely rotted after being placed in storage. In many cases 

 there occurs a characteristic splitting at the calyx end accompanied 

 by a discoloration and rotting of the surrounding tissue. The 

 fungus may gain entrance through wounds, resulting in a soft rot 

 of a light brown color, with a characteristic sunken area in the 

 center. This is essentially a ripe rot which works slowly, and is 

 often obscured by more rapid soft rot fungi. 



The fungus evidently passes the winter in the diseased fruit re- 

 maining in the orchard and in the spring infects the young fruit 

 either at the blossom end or through wounds. 



On the pear, the fungus is reported as being found on fruit, leaves 

 and young sprouts. 



Microscopic Characters. The mycelinl threads of the fungus vary 

 greatly in size and in the young stages are hyalin and septate. As 

 spores are produced they become brown in color. 



The spores are characteristic of the genus Alternaria. Under 

 the micr-oscope they appear brown in cohn* and vary in size from 

 12x4 microns to 17 x G. They vary in the number of cells ci)mi)Osing 

 them, having from 2 to 7 and averaging about H. They are i)ro,luced 

 either singly or in chains. 



riermination is very rapid, usually taking ])lace in from 10 to 

 15 hours, the germ tube being sent out from any cell or from several. 



Cultural Characteristics. The organism was found to grow 

 especially well on pear agar. On this medium. ;ui abmidant growth 

 was very ([uickly |)r(iduced and rapid spore pi'oduction took ]>la(e. 

 It was also found to grow fairly well on nutrient. ]>otato and 

 bean agar. Imt spore fonnation apjiearcd to be slower. On jHsn* 

 agiii- the colonies appeared in two days, the mycelial growth was 

 rajud, the colonies reaching a diameter of 2..") cm. in five days. The 



