344 Bulletin 73. 



Prunus virginiana ly. Choke Cherry. 

 Exoascus confusus n. sp. 



The fungus causing the hj-pertrophied fruits of Primus virgin- 

 iana have been referred, it seems to me improperly, to Exoasais 

 primi. Sadebeck* considers it identical with the Exoascus caus- 

 ing the hypertrophied fruits of P. domestica and places it in E. 

 prtiui. The asci are quite different and especially the stalk cells 

 and their proportion to the asci. Figures 37-39, Plate XII, 

 represent the details of these structures. Fig. 37 is from a rather 

 young specimen from Forest Home, N. Y., and figs. 38, 39, from 

 specimens collected by Underwood at Taburg, N. Y., communi- 

 cated by Seymour. Comparing these figures with those of 

 E- pruni ixovQ. P. domestica, shown in figs. 44, 45, a great differ- 

 ence is seen. All of these illustrations of the structure of the 

 asci, etc. , are carefully drawn with the aid of the camera lucida 

 to the same scale, so the comparison can well be made from the 

 illustrations. The asci of this species on the fruit of P. virginiana 

 are, according to these specimens, 30-45 long b}^ 8-12 in diam- 

 eter. The stalk cells are 15-30 high by 6-10 in diameter. 

 The stalk cells are nearly or quite the same diameter as the asci 

 and are proportionally longer than those of E. priini on P. domes- 

 tica, and Sadebeckf says upon examination that the fungus upon 

 the fruit of P. domestica in the United States is the same as that 

 in Europe upon the same host. The stalk cells also on the fruit 

 of P. domestica are also more slender in proportion to the diameter 

 of the ascus than in those on the fruit oi P. virginiana. 



The physiological effect upon the host is also quite different. 

 Not only is the hypertrophied fruit much longer in proportion to 

 the diameter than is the case with the fruit of P. dofiiestica, but 

 the floral envelopes are also constantly hypertrophied and become 

 persistent, which is not the case with the same organs of the 

 flower oi P. domestica. The asci are also developed on the floral 

 organs. 



*Kritische Unters, etc. Ab. a. d. Jahrb. d. Hamb. Wiss. Anst. VIII, 29, 

 1891. 

 tDie parasitischen Exoasceen. Ibid. X, 2, p. 44, 1893. 



