320 BUI.I.ETIN 73- 



in which the asci are developed from a common subcuticular h3^- 

 menium are farther divided into two genera. Those with a per- 

 ennial mycelium are placed in the Fuckelian genus Exoascus, 

 while those lacking a perennial mjxelium are placed in the Frie- 

 sian genus Taphrina. Taphrina as thus emended contains species 

 in which a new infection each year is brought about by spores. 

 A common representative of the genus in this country is T. coeru- 

 lescens'^ (Mont, et Desm.) Tub The species of Exoascus having 

 a perennial mycelium, a new infection each year is secured by the 

 mycelium which winters over in ^the tissues of the host, and by 

 the spores. 



The prunicolous species of Exoascea; thus far known all belong 

 to the genus Exoascus. These have for the present purpose the 

 chief interest and farther discussion of the other two genera is 

 not contemplated here. 



Considerable material has accumulated during a period of ob- 

 servation extending over five years, which seemed to justify the 

 preparation of the matter for publication. Especially does this 

 seem to be the case since no comprehensive illustrated account of 

 those species occurring on the stone fruits in the United States 

 has as yet been attempted. The economic importance of the 

 stone fruits suggested the appropriateness of presenting the con- 

 tribution as a bulletin for the information of fruit growers, since 

 a knowledge of the known characteristics and mode of perpetua- 

 tion of the parasites will aid those interested in checking or pre- 

 venting the injuries. 



In making a critical examination of the material at hand it 

 appeared that there were several well characterised undescribed 

 species, a fact which was not anticipated at the outset. This is a 

 sufficient explanation of the necessary use of much technical 

 description in a portion of the paper. 



No part of the plant is exempt from the attacks of these fungi 

 except the roots. The first marked effects of their active presence 

 in the tissues of the host is the stimulus to an increase in the 

 number or size of the cells so that characteristic malformations of 

 the diseased parts appear. In the leaves the increase in the num- 



*Ascomyces coerulescens Mont, et Desm. Ann. d. Sci. Nat. Bot. ser. 3, x. 

 p. 345. Taphrina coerulescens Tulasne, Ann. d. Sci. Nat. Bot. ser. 5, v. p. 127. 



