VOL. IV.] Reviezus. 409 



Die Parasiiischen Exoasceen. A Jlfojwgraph. By R. SadK- 

 BSCK. Hamburg, 1893. In the above monograph is presented 

 a very complete and accurate account of the peculiar group of 

 Fungi, the Exoasceae. The meaibers of this family are fungi of 

 extremel}' simple structure, and some of them are parasites that 

 cause serious trouble by their ravages. Probably the most 

 familiar species is Exoascus deformans (Berk.) Fuckel, the cause 

 of the well-known disease of peach trees popularly called " leaf- 

 curl." When the trees are severely attacked they sometimes 

 are almost completely stripped of their leaves, resulting in a 

 serious check to the tree's growth. 



The first section of Professor Sadebeck's monograph deals 

 with a comparative study of the development and biolog)^ of the 

 parasitic Exoascese. Although many experiments were made 

 with various species, none of the attempts to grow the spores 

 upon artificial culture media were entirely successful, and in no 

 ■cases was he able to produce spore-bearing plants in this way. 

 In some instances, however, he was able to follow the penetra- 

 tion of the host by the germ-hypha of the parasite, and to trace 

 its development within the host. The species especially studied 

 were Exoascus Tosquinctii (West) Sadeb., E. epiphyllus Sadeb., 

 Taphrina Sadebeckii Johans., as well as several other species of 

 Taphrina. In the species of Exoascus the mycelium is peren- 

 nial, and this insures the perpetuation of the fungus, even if for 

 any reason the spores should fail to germinate. 



The asci open by a cleft at the apex, and the spores are 

 violently ejected by the strong contraction of the side walls of 

 the ascus which are in a state of tension before it opens. Some- 

 times instead of the ordinary spores, 3'east-like conidia are 

 produced within the ascus, and in case the conditions are un- 

 favorable for the formation of either spores or conidia, e. g. 

 in very rainy weather, the asci form directly yeast-like conidia 

 by budding. 



Sadebeck separates the parasitic Exoascese into the genera 

 Exoascus Fuckel, TapJirina Fries, and Magniisiella Sadeb. 

 The first genus is characterized by the perennial mycelium and 

 the fact that the whole mycelium, or at least that part under the 

 cuticle of the infected leaf, breaks up into cells that develop 

 directly into asci. Twenty-one species are given. 



