APPLE DISEASES 11 



its food from the cuticle, water is drawn from adjacent cells as 

 evidenced by the one-sidedness of affected apples and in the 

 puffing of the leaves under the scab spots. 



The mycelium of the pathogene on the leaves and fruits 

 modifies its form slightly by transforming into a stroma, a 

 spore-bearing cushion. From this cushion arise spore-stalks, 

 conidiophores, which cut successively from the free outer end 

 several conidia asexual summer spores. These conidia 

 mature rapidly and are blown to other leaves and fruits, where 

 they produce scab spots just as described for the ascospores. 

 From these spots, caused by the growth from the conidia, arise 

 again the stromata on which a second crop of conidia are borne. 

 These are likewise capable of further spread of the pathogene. 

 This process repeats itself throughout the growing-season, 

 depending on conditions of moisture. If fruits are inoculated 

 just prior to picking, the spots appear in storage; their ap- 

 pearance has been described under Symptoms. Fruits which 

 fall carry the fungus with them, but the pathogene never devel- 

 ops further. Leaves, on the other hand, furnish the chief 

 hibernating quarters for the fungus. As soon as the foliage 

 falls, the mycelium of the organism penetrates all parts of the 

 leaves. During the autumn and early winter the perithecia 

 are partially formed, these organs lying dormant until spring. 

 At this time growth is resumed and the life-cycle is again ini- 

 tiated. There is considerable evidence that the conidia hiber- 

 nate on the twigs or in the bud-scales, but the old leaves on the 

 ground are to be regarded as the chief source of the primary 

 inoculum. 



Control of apple-scab. 



The destruction of fallen leaves would appear to lessen the 

 primary infection. But in actual practice that method alone 

 is not reliable and at best is only to supplement spraying or 

 dusting. Spraying is at present the chief method of control. 

 The fungicide used is lime-sulfur^stfmtion, diluted one gallon 



