ANTHEACNOSE OF CUCURBITS. 



27 



In some cases of delayed or, perhaps, inhibited penetration, there is 

 a swelling and- change of staining reaction of the cell wall under the 

 appressorium, characterized 

 by retention of the safranin 

 in the triple stain (fig. 8). 



The mode of fruit penetra- 

 tion appears to be somewhat 

 similar. Sections from fixa- 

 tions made two weeks after 

 inoculation show numerous 



Fig. 5. — Cross section through a stoma, show- 

 ing an appressorium formed directly with- 

 in the stomatal pore. Penetration of a 

 guard cell has occurred, 65 hours after in- 

 oculation. (Camera-lucida drawing; mag- 

 nified about 1,300 times.) 



Fig. 6. — Cross section of leaf epidermis and pali- 

 sade tissue, showing penetration of a stomatal 

 guard cell from an appressorium, emergence of 

 penetration rube into substomatal chamber, and 

 indentation of palisade cell by the swollen tip of 

 the tube. The wall of the palisade cell is swollen 

 and retains safranin in the area in contact with 

 the fungus; 65 hours after inoculation. (Camera* 

 lueida drawing; magnified about 5.70 times.) 



examples of direct penetration of the cuticle and thick outer 

 wall, but no cases of subsequent mycelial development. In view 

 of this fact, it seems likely that these are abortive or inhibited 

 penetrations. Fruit penetration is illustrated in figure 9. Here 



the penetration tube is not 

 as clearly distinguishable as 

 in the leaf sections, and only 

 the swollen tip is to be seen. 

 There is indication of a 

 splitting apart of the wall 

 layers in some cases, and all 

 cases are characterized by 

 a marked retention of the 

 safranin in the inner wall 

 layer under the appresso- 

 rium (fig. 9). 



The exact method of 

 cuticle penetration is not 

 yet understood. It is not 

 known whether the penetration of the cuticle proper is due to 

 mechanical pressure alone, as Blackman and Welsford (6) find in 

 Botrytis, or whether there is some softening in advance of actual 



Fig. 7. — Cross section of leaf epidermis, showing penetration 

 of an epidermal cell, 121 hours after inoculation. The con- 

 tents of the appressorium have apparently passed into the 

 penetration tube. Mycelial growth has begun from the 

 swollen tip of the latter. Division of the host nucleus has 

 occurred as a result of the fungous invasion. (Camera- 

 lucida drawing; magnified about 615 times.) 



