state pomological society. 35 



The Apple Scab Fungus. 



In order to freshen our memories a little, allow me to recite 

 briefly the life cycle of the apple scab fungus. The scab 

 disease is selected because it is the most important disease of 

 fungous origin that northern and eastern apple growers have to 

 fight. The habits of fungi in general are not so commonly 

 understood as those of insects, owing to the facts that most of 

 the important structures of fungi are microscopic in size and 

 that their devastating work has been done even before they 

 are apparent to the naked eye. 



Winter Stage. The fungus causing the scab of apples, as 

 you will recall, passes the winter in the infected, fallen leaves 

 on the ground. In New York state we have never been abiL 

 to discover any other stage by which the fungus gets through 

 the winter. Within the past few weeks, however, Doctor 

 Morse, of your Experiment Station, has recorded some very 

 interesting observations in which it seems quite certain that 

 the fungus has been able to hibernate on infected twigs of the 

 previous year. How generally such conditions may prevail 

 remains yet to be seen, but apparently this discovery will not 

 materially affect the method of scab control, inasmuch as ex- 

 perimental work in most of the eastern states has shown that 

 a proper application of fungicides as generally recommended is 

 effective. 



Spoi'e Discharge and Dissemination. The fact that the 

 scat) fungus certainly passes the winter on the fallen leaves 

 leads at once to the question of how the organism is able to get 

 from the ground to the developing foliage and fruit of the 

 tree. The way in which this is accomplished is exceedingly 

 interesting, but to be appreciated fully, should be observed 

 under the microscope. An examination of old leaves in the 

 early spring often reveals the presence of minute globose 

 bodies developed within the tissue of the leaf. These bodies 

 are exceedingly small and for the most part are barely large 

 enough to be detected with the naked eye. With the occur- 

 rence of the spring rains, these bodies increase slightly in size 

 and break through the epidermis of the leaf on the side which 

 happens to be lying upward. Doctor Wallace, who was for- 

 merly a student with us, has followed the development of this 



