ORDER TAPHRINALES (eXOASCALES) 241 



The relationship of this order is more or less in dispute. The compact 

 hymenium, with numerous well-developed paraphyses, and the slit-like 

 opening suggest great affinity to some of the Phacidiaceae, as does the 

 great variability of ascospore structure. The suggested relationship to 

 the family Lophiostomataceae in the Order Sphaeriales seems doubtful, 

 in spite of the slit-like ostiole, for in other respects the latter family is 

 typically Sphaeriaceous. 



Order Taphrinales (Exoascales). This is a group of approximately 100 

 recognized species of fungi, all but a very few parasitic. Tw^o or more 

 genera are recognized in two families whose actual relationship to one 

 another is uncertain. Both families are characterized by the production 

 of a superficial hymenium with indeterminate margin and without para- 

 physes. This may rest upon a thin membranous hypothecium consisting 

 of interwoven hyphae (Ascocorticiaceae) or may burst through the epi- 

 dermis or cuticle of the host plant without a definite hypothecium 

 (Taphrinaceae). In the author's opinion these represent the ultimate 

 steps in the reduction and simplification of an apothecium. Together with 

 this simplification of apothecial structure there has arisen a marked 

 modification of the sexual process in the Taphrinaceae. According to 

 Miss Wieben (1927) the life history for Taphrina epiphylla Sadeb. and 

 T. klcbalmi Wieben is as follows: An ascospore, or one of the smaller 

 spores which the ascospores may produce by budding while still within 

 the ascus, germinates upon the surface of the host plant. Only when the 

 germ tubes from two such spores of opposite sexual phase meet and fuse 

 is active infection of the host possible. As a result of this conjugation a 

 dicaryon hypha is produced which grows intercellularly in the host tissues. 

 R. E. Fitzpatrick (1934) has shown that in T. deformans (Berk.) Tul. a 

 single spore can cause infection. The nucleus of this spore divides and 

 thenceforth the two nuclei divide conjugately and the vegetative my- 

 celium is of dicaryon nature as in the case of the species studied by 

 Miss Wieben. 



The presence of these hyphae causes hypertrophy and hyperplasia in 

 the affected parts of the host. This may affect the leaves, fruits, and 

 shoots, often causing the formation of "witches' brooms." Eventually 

 dicaryon cells are formed near the surface of the host, often in a sub- 

 cuticular location, forming a structure resembling pavement epithehum. 

 These cells sometimes become somewhat thick-Avalled. In them eventually 

 jnuclear fusion occurs, followed by elongation of the cell in a vertical 

 lirection, rupturing the cuticle or emerging between epidermal cells of 

 bhe host. The diploid nucleus and most of the cytoplasm pass into the 

 [upper part of the cell leaving an empty lower part which is sometimes 

 [but not always cut off from the upper part by a cross wall, or the diploid 

 [nucleus may divide and one remain in the lower cell while the other passes 



