1908.] Apple "Scab" or "Black Spot." 



185 



the cell-sap ; at the surface of the leaf it sends out into 

 the air short branches, at the ends of which the minute 

 dark-brown spores, or conidia, are produced. (Fig. 5c). 

 Some millions of these minute spores are produced at each 

 " sooty " place on an apple leaf, and each spore on being 

 carried by the wind or rain, or by insects, to the fruit is able 

 to infect it at once, and produce on it the " scab " or 

 " black spot." 



fig. 3. — The Apple Scab or "Black 

 Spot " fungus attacking the leaf. The 

 dark-brown " sooty " patches of the 

 fungus follow more or less the course of 

 the veins of the leaf. 



fig. 4. — The Apple Scab or "Black 

 Spot " fungus attacking the leaf. " War- 

 ner's King " ; the dark-brown " sooty " 

 patches of the fungus occur on little 

 swellings on the upper surface of the leaf. 



It is chiefly in consequence of the grower allowing the fungus 

 to increase on the leaves and to produce there its millions of 

 spores, instead of keeping the leaves healthy by spraying, 

 that his apples become " scabby " each season. Other injury, 

 too, apart from the infection of the fruit may result. If the 

 leaves are severely attacked, a premature shedding of the 

 foliage results, with a marked injurious effect on the season's 

 growth of the tree. 



But, not uncommonly, another annual source of infection 



