ANTHRACNOSE OE CUCURBITS. 21 



ture of 30° C. swollen "involution forms" were produced in the 

 Van Tieghem cells. 



The minimum temperature permitting germination was 4° C. in 

 exposed drops of prune decoction, 7° in exposed drops of water, and 

 14° in hanging drops in either medium. The optimum temperature 

 for germination apparently lies between 22° and 27° C. Edgerton 

 (14) found that the optimum temperature for mycelial growth was 

 24° C. It is of interest to note here that at temperatures of 20°, 

 22 °, and 27° C. the fungus in the exposed drop of prune juice com- 

 pleted its life cycle in four days with the production of sporulating 

 acervuli. In the hanging drop of the same medium at 27° and in 

 exposed drops at 16° C, seven days were required to complete the 

 cycle. 



Germination is favored, therefore, by the presence of nutrient 

 material, by a good oxygen supply or at least good aeration, and 

 by temperatures of 22° to 27° C. 



AtPRESSORIUM FORMATION. 



As to the factors influencing the formation of appressoria in general, 

 De Bary (2) held that, in Sclerotinia, appressoria were the result of 

 a contact stimulus, and his opinion was corroborated by Biisgen (7), 

 who worked with several parasitic fungi. Halsted (24) found that 

 appressoria were generally produced by Gloeosporium and Colletot- 

 richum. American writers in general have called them secondary 

 spores or chlamydospores (26). Hasselbring (26), working with the 

 fungus of apple bitter-rot, found tha^t appressoria were formed only 

 as a result of a contact stimulus in a medium poor in food supply. 

 Appressoria were never formed until the germ tube came into con- 

 tact with the glass, and not even then when in a nutrient medium. 

 He found also that the appressoria tended to adhere to the glass. 



In the course of this work some effort was made to throw further 

 light on the factors controlling appressorium formation. In the 

 germination tests mentioned above it was noted that the appres- 

 soria were usually but not always formed in contact with the glass. 

 They occurred in the hanging drops usually up against the glass 

 and were not as abundant as in the exposed drops. Appressoria 

 were formed just as commonly in the nutrient prune decoction as in 

 the distilled water. 



It was noted that the formation of appressoria in exposed drops, as 

 well as in hanging drops, occurred most readily about the margin 

 of the drop. Furthermore, their formation in hanging drops of 

 water was more general than in the hanging drops of prune decoction. 

 In exposed drops of prune juice appressoria were formed at tempera- 

 tures from 9° to 27° C. ; in hanging drops, only between 17° and 20°. 

 In exposed drops of water appressoria were formed between 12° and 



