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TEXTBOOK OF BOTANY 



able on the leaves, fruits, and flower pedicels (Fig. 260). These spots 

 not only lessen the commercial value of the fruit, but also decrease photo- 

 synthesis, cause early abscission of fruits and leaves, and check the 

 growth of the remaining apples. The mature ascospores in the old dead 

 leaves on the ground are projected into the air from the bursting asci 

 during rainv weather in the spring and are blown about by the wind to 



j&itk * ,^ll 



Fig. 260. Apple seal): A, on the fruit; B, on a leaf in which the fungus lives 

 throughout the winter; C, magnified section of an ascocarp with asci and asco- 

 spores from an over-wintered leaf; D, ascocarps visible in an old leaf after it has 

 been cleared in hot potassium hydroxide. Adapted in part from A. L. Pierstorff 

 and Ohio Agricultural Extension Sendee. 



the apple trees. The spores germinate almost immediately on the living 

 tissues of opening buds, young leaves, and flowers if a film of water is 

 present. Sprays of lime sulfur, or wettable sulfur, must be applied before 

 extended periods of rain to prevent infection by the hyphae from the 

 germinated ascospores. After infection and growth of an internal my- 

 celium, conidia develop and are distributed to other parts of the tree 

 by rain water. 



It is extremely desirable that all pre-blossom infections of apple scab 

 be prevented, since conidia may be produced all summer long from 

 hyphae of mycelia if the early infection by ascospores is allowed to 



