ASCOMYCETES 175 



The families of the Discomycetes (or discomycete-like forms) 

 which are here of interest are Exoascaceae, Helotiaceae, Mol- 

 lisiaceae, and Phacidiaceae. The Pyrenomycetes from which im- 

 portant parasitic representatives have been selected are the 

 Perisporiaceae, Erysiphaceae, Hypocreaceae, Dothidiaceae, Myco- 

 spherellaceae, Pleosporaceae, Gnomoniaceae, and Diatrypaceae. 



I. EXOASCACEAE 



ATKINSON, G. F. Leaf Curl and Plum Pockets. Cornell Univ. Agl. Exp. Sta. 



Built. 73: 319-355. pis. 1-20. 1894. 

 PATTERSON, FLORA W. A Study of North Am. Parasitic Exoasceae. Labs. 



Natural Hist, Univ. of Iowa Built. 3: 89-135. pis. 1-4. 1895. 

 RATHAY, E. Ueber die Hexenbesen der Kirschbaume und iiber Exoasctis 



Wiesneri n. sp. Sitzber. d. kaisl. Akademie d. Wiss. 83 : 267-288. pis. 



1,2. 1881. 

 ROBINSON, B. L. Notes on the Genus Taphrina. Ann. Bot. 1 : 163-176. 



1887. 

 SADEBECK, R. Die parasitischen Exoasceen. Eine Monographic (Arb. d. bot. 



Museums zu Hamburg). 1893. 

 SADEBECK, R. Einige neue Beobachtungen und kritische Bemerkungen iiber 



d. Exoascaceae. Ber. d. deut. bot. Ges. 13: 265-280. pi. 21. 1895. 

 SCHROETER, J. Exoascaceae. Pflanzenfamilien (Engler u. Prantl) 1 (i* Abt.): 



158-161. fig. 136. 1894. 



The Exoascaceae are parasitic fungi causing slight or very 

 marked abnormalities of the leaves, fruits, etc., of a variety of 

 plants, mostly woody forms. The deformities are commonly of 

 the nature of leaf curls, malformed fruits (such as plum pockets), 

 and witches' brooms. Such diseases are especially common among 

 the stone fruits. This family of fungi is considered by many to 

 be closely related to the lowest Discomycetes. In the Exoas- 

 caceae, however, the asci are produced on the surface of the host, 

 arising directly from the mycelium, without the development of 

 a distinct, complex, basal structure, or hymenial layer. Each ascus 

 may possess a stalk cell or it may be merely cut off by a cross 

 wall from a hypha growing perpendicular to the surface. An 

 ascus usually contains eight spores, which in some cases bud ex- 

 tensively in a yeast-like manner, even within the ascus. 



In the genus Exoascus, which embraces those forms of greatest 

 economic importance in the family, there are almost constantly 

 eight spores, and budding seldom occurs prior to the expulsion 

 of the spores from the ascus. 



