ANTHRACNOSE OF CUCURBITS. 17 



branch thereof. The appressoria are brown, thick-walled, ovoid to 

 spherical cells, in general appearance not unlike the intercalary 

 chlamydospores of the mycelium. The analogy between these 

 appressoria and chlamydospores is strikingly shown in cases where 

 appressoria are formed in series, one apparently budding out to 

 form another. The appressorium may taper slightly toward the 

 point of attachment of the germ tube and may be flattened on the 

 side in contact with the substratum. 



A definite round germ pore is found in the center of the lower side of 

 an appressorium from which leaf penetration has occurred. For all 

 of the strains studied, the size and shape of the appressoria seem to 

 be quite uniform. In a few cases appressoria have been observed 

 to increase considerably in size and become two celled. 



CULTURAL CHARACTERS. 



Carsner 1 has described the cultural characters somewhat at 

 length. No effort has been made in this work to compare the growth 

 on different media. For general purposes a 2J per cent water agar 

 containing 2 per cent of dextrose has proved very useful. Besides 

 this, potato, bean, and apple-twig agar have been used. The fungus 

 grows rapidly and is easily cultured. 



Isolation from diseased specimens was usually accomplished by 

 first transferring spores from the acervuli to a drop of sterile water 

 on a flamed slide. From this drop loop inoculations were made 

 into tubes of melted agar. Plates we.re poured and transfers made 

 from single colonies developing therein. Many of the strains were 

 grown from a single spore. 



There is great variation among different strains in the amount of 

 aerial growth, the extent of the blackening, and the abundance of 

 sporulation. Cultural characteristics tend to change during pro- 

 longed propagation, as has been noted in other anthracnose fungi by 

 Edgerton (12, p. 393). The strains longest in culture seem to spor- 

 ulate most abundantly. Sporulation can be readily secured by the 

 use of sterilized segments of cucumber stems. 



In test-tube culture the mycelium is first white or colorless, later 

 pink, and finally black. The aerial growth usually becomes pros- 

 trate quite promptly. Acervuli appear first as black points and 

 sporulation occurs within a week. The pink spore masses may be 

 formed for several weeks. In old cultures the black sclerotial 

 bodies are prominent on the surface and also scattered through the 

 medium to some depth. General blackening of the mycelium may 

 extend to some depth also. 



i Carsner, E. Op. cit. 

 69806°— 18— Bull. 727 3 



