PEACH SCAB AND ITS CONTEOL. 43 



do the earlier infections of twigs and leaves. No other source of 

 infection is known to be available until sporulation occurs on lesions 

 of the current year's production. In northern Georgia this does not 

 usually take place to any considerable degree until early June. 



Secondary. — Conidia from lesions of the current year's production 

 constitute the source of secondary infection. On account of the 

 long period of incubation of the fungus, lesions resulting from this 

 type of infection rarely become injurious on the fruit, except, perhaps, 

 on late varieties. On the twigs and leaves, however, as was demon- 

 strated in the inoculation experiments, secondary infections may be 

 very abundant. Under orchard conditions such infections un- 

 doubtedly accoimt for a large percentage of the twig and leaf lesions 

 which appear throughout the late summer and fall. 



OVERWINTERING OF THE FUNGUS. 



In considering the problem of how the fungus passes the winter, 

 three major possibiUties demand attention, viz, (1) the overwintering 

 of conidia, (2) the overwintering of the myceUmn in dead infected 

 parts, and (3) the overwintering of the myceUum in lesions upon the 

 living host. 



Careful studies of infected fruits, twigs, and leaves in late winter 

 uniformly failed to reveal the presence of viable conidia. Further- 

 more, the evidence furnished by the germination tests previously 

 reported shows conclusively that when exposed under orchard con- 

 ditions these conidia would not remain dormant and viable over 

 winter. Even if they did pass the winter in minimal numbers, the 

 conditions of infection, as set forth above, would make them a neg- 

 ligible factor in the life history of the fungus. 



In the fall of 1913, portions of diseased fruits, twigs, and leaves from 

 CorneHa, Ga., were exposed in the university orchard at Madison, 

 Wis., and allowed to pass the winter. In the following spring conidia 

 were produced in considerable numbers upon the fruit and twig frag- 

 ments, and the fungus was readily isolated from each of these sources. 

 The leaves, however, were badly decomposed, and the fungus was not 

 identified upon them. 



At Cornelia, Ga., during the springs of 1912 and 1913, many over- 

 wintered fruits and leaves from trees and from the ground were 

 examined microscopically. The fungus was not definitely identified 

 from any of these sources. It is quite probable, however, that under 

 favorable circumstances the mycelium may survive the winter under 

 orchard conditions upon fallen fruits, twigs, or leaves; but the 

 evidence previously cited seems to prove conclusively that this type 

 of overwintering is of no practical significance in the life history of 

 the fungus. 



