MICHIGAN ACADEMY OF SCIENCE. 97 



the plant was not growing fast enough to cause the large split 

 seen under Held conditions. The infection did not seem to extend 

 deep into the stem nor far from the spot of puncture and it is 

 likely that many of the lesions seen in the field are not entirely 

 due to the fungus but also to the tendency of the stem to crack 

 open when injured during rai)id growth. 



Leaf InoeitJatioiis: 



Leaf infection was secured only where the plant was actually 

 punctured and then in only a few cases. The infected spot became 

 lighter in color and then gradually developed a translucent, brown 

 appearance. This spot took up about one-half the leaf and soon 

 became shriveled and water-soaked. The spores were borne 

 sparsely on the surface but could be seen only microscopically. 



The water-soaked, blackened appearance sometimes found in the 

 field, is possibly due to outside infection with soft rots of some 

 sort. The tissues are softened and the cell walls more or less dis- 

 solved so that the leaf would form a very susceptible medium for 

 such infection. The writer has never seen this condition produced 

 in plants inoculated with Cladosporium cucumerinum, nor does it 

 appear to be a constant character in the field. 



Inoculation of the Fruit: 



With the fiiiit the same factor of mechanical injury was noted. 

 Where the spores were sprayed on the fruit the successful inocula- 

 tions were relatively few, while when injured they were almost 

 universally successful. 



The first sign of infection is a water-soaked spot accompanied by 

 a gummy exudate, due to the dissolving action of the mycelium on 

 the cells of its host. This appears about 48 hours to 72 houi"s 

 after inoculation and becomes gradually more sunken until the 

 fung-us growth covers the surface and the entire epidermis is de- 

 stroyed, being replaced by the mass of fruiting hyphae which give 

 the olive black color to the infected spot. 



The myeclium of the fungus as seen in stained sections does not 

 penetrate the cells but exerts a dissolving action upon them. A 

 cavity is formed beneath the epidermis and the mycelium is found 

 pressed closely against the walls of the gi-adually disintegrating 

 cells. This mycelium grows in a medium composed of the products 

 of this cellular decomposition and in section we see the strands of 

 mycelium massed around the edge of the cavity and intermixed 

 with the gum and fragments of the broken cell walls. After the 

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