334 Notes on Parasitic Ascomycetes. [Sess. 



the host-plant. The cuticle is finally ruptured, and the asci 

 become fully exposed to the air, without being enclosed in 

 any kind of receptacle. They are usually packed closely 

 side by side, and are often so numerous as to impart a 

 glaucous or bloom-like appearance to the surface on which 

 they grow. The asci contain at first 8 spores, but the 

 latter in many species produce by a budding process secondary 

 spores in such numbers as completely to fill the ascus. In 

 this family there are two genera — viz., Exoascus and Taphrina. 

 In Exoascus the mycelium is perennial in the young shoots 

 of the host, passes annually into the growing buds, and is 

 at length developed in the leaves or fruit. In Ta'phrina, 

 however, the mycelium is not perennial, but is annually 

 developed in the leaves, owing to fresh infection having 

 taken place. 



The most notable species in these two genera are the 

 following : — 



Exoascus deformans (Berk.) Fckl. produces on peach-trees 

 the disease known as '* leaf-curl." The affected leaves become 

 enlarged, much crumpled and twisted, usually more or less 

 rosy in colour, and covered with a whitish bloom, owing 

 to the number of asci exposed on their surface. 



E. pruni (Tul.) Fckl. attacks the immature fruit of the 

 plum, sloe, and bird-cherry. It arrests the development of 

 the stone and embryo, and stimulates the mesocarp to 

 excessive growth, so that the fruit becomes much elongated 

 and swollen, and bears on its surface the asci characteristic 

 of the fungus. 



E. turgidus Sadeb. produces on birch - trees those con- 

 spicuously crowded clusters of undersized branches known 

 as " witches'-brooms," which are common in most parts of 

 the country. The asci are developed on the leaves borne 

 by the branchlets forming the besom. These growths, how- 

 ever, have to be distinguished from the smaller besoms 

 frequently produced on birch- trees by Eriophyes rudis Nal., 

 a parasitic mite which is sometimes also present in the 

 clusters originally formed by the Exoascus. 



E. carpini Eostr. produces witches'-brooms on hornbeam- 

 trees similar to those just referred to as common on birch, 

 but is of much less frequent occurrence. 



