BEOWN-ROT OF PRUNES AND CHERRIES. 3 



conditions were such as to indicate that the brown-rot organism was 

 an important factor in the case. 



In the spring of 1915 the prune orchards in the vicinity of Van- 

 couver, Wash., were kept under close observation, and a record was 

 made of orchard and weather conditions. March 28 and 30 v/ere fair 

 days, but with these exceptions it rained almost continuously from 

 March 24 to April 8. The trees were in full bloom on March 23, and 

 on April 5 the blossoms were falling. On the latter date there was no 

 evidence of typical blossom blight as it usually occurs in eastern sec- 

 tions, but many of the calyx cups were turning brown on the under 

 side where drops of water had hung, and the margins of the sepals were 

 often similarly affected. On April 8 some of the young fruit was turn- 

 ing yellow and dropping, apparently from lack of fertilization of the 

 blossoms. At this time the browning of the calyxes had become much, 

 more serious, involving in some cases more than three-fourths of the 

 crop of the unsprayed trees. It was much more abundant on the 

 lower than on the upper branches and seemed to be as common on 

 the fertilized as on the unfertilized fruit. In some cases the brown- 

 ing spread down the pedicel, the fruit often turning back on its stem; 

 in others it involved most of the calyx, the young fruit separating 

 readily from it. (PI. I, figs. 4, 5, and 6.) The latter condition was 

 more common on the fertilized blossoms. When placed in a moist 

 chamber, the ailected fruit developed an abundant growth of Monilia, 

 the conidial stage of Sclerotinia cinerea (Bon.) Wor.* 



On April 12 a heavy drop was taking place, both of the unfertilized 

 and the fertilized but infected fruit. At this time the fertilized fruit 

 could be readily distinguished from the apparently unfertilized by 

 its enlarged ovary, its lengthened pedicel, and its darker green color. 



The brown-rot fungus produces two distinct types of spores — one, 

 the Monilia or summer form, which gives the characteristic mouse- 

 colored appearance to the rotting fruit; the other, the mature or 

 perfect stage, in which the spores are borne on the upper surface of 

 cup-shaped fruiting bodies, known as apothecia, that develop from 

 the mummied prunes. 



On April 2 apothecia were evident under the trees on the diseased 

 prunes of previous seasons. By April 8 they had developed in large 

 numbers, 30 to 40 clusters often being found on the ground under one 

 tree. (PI. I, fig. 3.) On the latter date many of the apothecia had 

 shed their spores, and by April 12 they were disappearing. Most of 

 the apothecia came from prunes near the surface of the soil, and while 

 some had unusually long stalks none could be found coming from a 

 greater depth than 3 or 4 inches. 



1 Matheny, W. A. A comparison of the American bro'vm-rot fungus with Sclerotinia fructigena and 

 S. cinerea of Europe. In Bot. Gaz., v, 56, no. 5^ p. 418-432, 6 fig. 1913. 



