296 MANUAL OF FRUIT DISEASES 



grown in higher places are more free from scab than those in 

 low areas. 



The twigs have more or less circular blotches of a yellowish 

 brown color, with a dark-gray or bluish border. Frequently 

 the spots become confluent, masking the normal pink-brown 

 color of the young bark. The cuticle is separated from the 

 cells beneath, corky cells are developed under the lesion, 

 and in some cases the cambium is killed, and as a result the 

 twig dies. 



That portion of the leaves of the peach lying midway be- 

 tween the main veins is especially affected. Brown, scattering 

 spots are developed in which the tissue dries up and finally 

 falls away, leaving circular holes. 



Cause. 



Peach-scab is caused by the fungus Cladosporium carpophilum. 

 Its mycelium occupies the space left by the partial separation 

 of the cuticle from the underlying cells. On the twigs the 

 mycelium hibernates in the form of dark-brown spherical 

 cells. It is possible that conidia lying about the lesions may 

 also be capable of tiding the fungus over winter. From the 

 resting-cells described above, conidia are produced in the 

 spring, and the latter are carried to the leaves and fruits. Ger- 

 mination follows shortly and penetration is effected. Inocu- 

 lation begins four to five weeks after the petals fall, but symp- 

 toms do not show to the naked eye for about three weeks subse- 

 quently. Inoculations and infections continue to take place 

 until about one month before the fruit matures. As the fungus 

 grows on the fruit the mycelium attaches itself closely to the 

 surface between the hairs, forming a mat of short, plump cells 

 which give rise to conidiophores and conidia. The flesh of 

 the peach is not penetrated, but the close contact of the fungus 

 with the outer cells allows absorption of nutrition from the 

 fruit through the unbroken walls. Evidently there is some 

 injury to the outer cells, for a cork-layer is developed just 



