APPLE DISEASES. 193 



when grown on prune agar, it would belong to the genus 

 Clasterosporimn of the Dematiacese. 



The fungus has been grown on a number of the common 

 culture media. It grows well and produces spores abundantly 

 in plates of prune agar, bean agar and potato agar. Consider- 

 able aerial mycelium is produced in each case which differs in 

 color on the different media being almost white on bean and 

 potato agars and dark brownish gray on prune agar. The cen- 

 tral part of the colony is wet and slimy in each case with no 

 aerial mycelium. The spores are produced in such numbers 

 as to form dense black masses. In the bean agar plates the 

 black spore masses were formed in concentric rings. The 

 fungus seems to fruit just as well when the colonies are 

 crowded in the petri dish as when only one colony is present. 

 Plates of prune agar were sown with spores so that from 30 

 to 100 colonies developed in a plate. The colonies did not 

 merge together but were separated by quite clear-cut lines 

 where they approached each other. The aerial mycelium was 

 well developed and these colonies formed spores. 



The mycelium of the fungus consists of large threads from 

 which finer branches are given off and is shown well by Fig. 

 37 which is a photomicrograph of mycelium from a prune agar 

 culture. The hyph^e vary in width from 1.5 to 8 microns, and 

 the length of the cells varies greatly, being from 11 to 80 

 microns for the most part although, in some cases, the actively 

 growing terminal end of a hypha is seen which shows no cross 

 wall in more than 200 microns. Not much difference can be 

 noted in structural characters of the mycelium on different cul- 

 ture media as measurements of hyphse from a number of media 

 gave the same results. 



There is, however, considerable variation in the spores in 

 culture as has been pointed out by Hartley for prune agar cul- 

 tures. Smith (5) has shown that the same kind of variations 

 takes place in the spores of C. bcycrinkii and Butler 

 (i) has described and figured the same thing for C. mori. 

 The spores of C. foliicolum taken from either apple leaf- 

 spot or canker do not vary greatly in size or number of cells. 

 They are for the most part four celled and measure 4-5.5 x 

 13-16.5 microns. On sterilized bean pods, potato cylinders, and 

 apple twigs in tubes, the spores are for the most part typical 



d 



