H. WORMALD 179 



which the conidia are produced be taken into consideration. The range 

 of variation and the average size of the conidia of the blossom-wilt 

 fungus under certain conditions is indicated in the accompanying table : 



Dimensions of the Conidia of fhe Blossom-Wilt Monilia. 



Source of conidia Range of variation Average 



Spurs and cankers in winter and spring 7 x 5 to 20 x 13 m 11*5 x 8-5 /^ 



(usually 10-14 x 7-9-5 m) 

 Young apples in the open in summer (June x 7-5 to 25 x 17/(;i 18 x 13 m 



and July) (usually lG-20 x 11-14-5^1) 



Potato cultures at temperature of laboratory 9x 7 to 26 x 20 fi 18-5 x 14-5 ;tc 



(15°-18° C.) (usually 16-20 x 11-14-5 m) 



When this fungus is growing on young apples in the open or on 

 steamed potato in the laboratory the dimensions of the conidia approach 

 those of M. frxctigena, but the smaller size and grey colour of the 

 pustules distinguish it from the latter. 



Strains of grey Monilias on plums show a similar variation as here 



shown : 



Average of 100 conidia Average of 100 conidia 

 from original source taken from culture 

 Strains of grey Monilias from plums of strain on steamed potato 



Strain VII, mummied plum, February 11-5 x 8-0 ^ 16-0 x 12-5 ytt 



VIII „ „ April " 11-5 X 8-Om 16-0 x 120m 



IX „ „ April 12-0 X 8-0 M 17-0 x 12-0 m 



X, dead twig, June 140 x 10-5 m 16-5 x 12-0 m 



XI, yoflng green plum, June 16-0 x 10-0 m 16-0 x 12-0 m 



XII, canker on plum tree, August no pustules present 1.5-5 x 11-5 m 



XIII, mature plums, August 14-5 x 11-0 m 1-'5-5 x 11-5m 



Strain VIII on prune-juice agar produced a browning of the medium 

 comparable with that caused by the blossom-wilt form of apples; the 

 others remained hyaline except Strains X and XI which were inter- 

 mediate in this respect, the coloration being less pronounced (hardly 

 perceptible in plate cultures) than in Strain VIII. 



These strains from plums generally produced conidia more readily 

 on steamed potato than did those from apple spurs and cankers; the 

 conidial tufts of the latter w^ere always scanty whereas the former may 

 produce definite concentric circles of conidiophores. 



Four strains have been isolated from Morello (acid) cherries and 

 though they have not yet been closely studied they behave in cultures 

 as the Strains X and XI from plums. 



Monilia fructigena shows less variation in the size of its conidia but 

 I have not yet found this species producing fresh chains of conidia in 



