PEACH SCAB AND ITS CONTROL. 



9 



contrast, the fungal tissue took up the red and orange quite freely, 

 while the dividing cells of the cork-forming layers stained a striking 

 hlue and the normal host cells below a bright 

 led. 



Fruit lesions. — In the early stages of fruit 

 infection the slender, branching, hyaline, 

 septate hyphse of thefimgus are found closely 

 appressed to the inner walls of the irregular 

 surface ceUs of the host. This early develop- 

 ment is most abundant in the minute depres- 

 sions about the bases of the hairs, where 

 conditions seem to be particularly favorable 

 tor the development of the parasite (fig. 1). 

 As the fungus becomes firmly estabhshed, 

 conidiophores are produced, while the vege- 

 tative hyphse branch and thicken until they 

 may entirely cover the area of infection. 

 The individual cells thicken and darken, 

 while transverse and longitudinal divisions 

 take place, often resulting in the formation 

 of irregular fungal masses five or six cells in 

 depth (fig. 2, a). This later development, 

 too, is particularly abundant in the depres- 

 sions about the bases of hairs. 



As the fungus develops generally over the sur- 

 face of the infected areas, the superficial host 

 cells die and the lesions may be cut off from the 



sound tissues below by the formation of pro- 

 tective layers of cork (fig. 2, l). These layers 

 are formed as the result of tangential divi- 

 sions of the subepi- 

 dermal cells. Less 

 frequently, trans- 

 verse divisions oc- 

 cur. Cork forma- 

 tion is usually most 

 vigorous in the third 

 or fourth subepi- 

 dermal layers and 

 ordinarily extends 

 slightly above and 

 below this actively 

 dividing region. 



In the case of early varieties of peaches, the fruits usually mature 

 before cork formation occurs. Upon later varieties, however, the 

 48408°— Boll. 395—17 2 



Fig. 1. — Section of a lesion from 

 an Elberta peach fruit, showing 

 the early development of the 

 parasite about the base of a 

 hair, in close contact with the 

 in Tier walls of adjacent surface 

 cells of the host . Camera-lucida 

 drawing. (Magnified 465 times.) 



Fig. 2.— Sections oi tesions from Elberta peach fruits: a. Shortly before 

 cork formation; h, soon after cork formation. At the right the section 

 extends nearly to the edge of the corky layer. Camera-lucida drawings. 

 (Magnifled 310 times.) 



