172 



Bulletin 395 



take the place of the phloem and the inner cortex. In cross section this 

 group of cells is wedge-shaped, with the apex extending toward the center 

 of the cane, and in the outer edge small bundles of fibers frequently may- 

 be observed. This tissue collapses soon after development and is torn 

 apart when the fissures occur in the lesion. 



CULTURAL CHARACTERS 



Miss Stoneman (1898) states that this fungus "does not adapt itself 

 readily to artificial culture, and considerable difficulty was experienced 

 before obtaining a pure culture." In making plantings of diseased tissue 

 the writer found that the fungus develops so slowly that contaminations 



are likely to grow 

 over it . The 

 growth of the or- 

 ganism from such 

 plantings cannot 

 be detected mi- 

 croscopically for 

 five or six days, 

 and a week more 

 is required for 

 sufficient develop- 

 ment before the 

 fungus can be re- 

 moved to a test 

 tube. Spore dilu- 

 tion plates are as 

 satisfactory a 

 method of isolat- 

 ing the pathogene 



as any, and conidia are readily obtainable throughout the summer and 

 even late in the autumn. A pure culture of the fungus may be obtained 

 also by inverting a sterilized petri dish containing a thin layer of nutrient 

 agar over a small piece of raspberry cane bearing ascocarps. When the 

 piece of bark is moistened the ascospores are ejected from the asci and 

 lodge on the agar surface above. The spores can then be located easily 

 with a low-magnifying microscope. By marking the position of the spores 

 on the lower side of the petri dish their germination and development can 

 be observed. The ascospores first produce sprout conidia, but further 

 development on the medium is identical with that from the conidia of 



the fungus. 



282 



Fig. 18. CONIDIA of plectodiscella veneta 



The conidia and conidiophores were produced in culture. Some of the conidia 

 are germinating. X 1132 



