LEAF CURL AND PLUM POCKETS. 



CONTRIBUTION TO THE KNOWLEDGE OF THE PRU- 

 NICOLOUS EXOASCE^ OF THE UNITED STATES. 



The distortions of the leaves of the genus Primus known 

 popularly as leaf curl, and the hollow, spongj^ abnormally en- 

 larged fruits commonly called "plum pockets," or "plum blad- 

 ders," are caused by certain fungi belonging to the family 

 Exoascecc. The Exoascea are composed largely of parasitic species 

 which live upon many of the higher plants and are especially 

 abundant upon the Rosacea;. The family is characterized by the 

 possession of fruit structures, termed asci, which are approximately 

 cylindrical and stand, more or less crowded together, out upon 

 the surface of the affected portions of their hosts. 



Several attempts have been made to establish genera for what 

 seemed to be natural divisions into which the members of the 

 family grouped themselves. These genera were based principally 

 upon the number of spores in the ascus. The known spore char- 

 acters, however, in this family are so remarkably inconstant that 

 nothing more than an unsatisfactory artificial classification has 

 thus far been proposed upon that basis. Sadebeck"^ has recently 

 proposed a more natural subdivision of the parasitic Exoascea. 

 Those species in which the asci are not developed from a common 

 subcuticular hymenium, but from the ends of intercellular hyphae 

 are made the ground for a new genus, Magnusiella. This genus 

 is represented in the United States by the well known M. poten- 

 tillce^ (Farl.) Sadeb., upon Potentilla canadensis. Those species 



* Die parasitischen Exoasceen. Eine Monographic. Abgedruck. a. d. 

 Jahrbuch d. Hatub. Wiss. Anstalten. x. 2. Hamburg, 1893. 



t Exoascus deformans (Berk.) Fuckel var. potentillae Farlow, Proceedings 

 Amer. Acad. Arts and Sciences, XVIII, 1883, p. 84. Taphrina potentillae 

 Jobanson, Oefvers. af. Kgl. Vet.-Akad Forh. 18S5. Magnusiella potentilla? 

 Sadeb. Abgedr. a. d. Jahrb. d. Hamb. Wiss. Anst. x. 2. 1893, p. 86. 



