21 



size of the perithecia, the length of the appendages, the number and 

 size of the asci, and the size of the sporidia ; but none of these forms 

 seem constant enough to justify their separation. On Liriodendron 

 the mycelium is usually inconspicuous, the appendages but little longer 

 than the diameter of the perithecium, and the few (8-10) asci are 

 large and broadly ovate.^ On Ulmus the mycelium is abundant and 

 persistent, the perithecia and appendages medium, and the very 

 numerous (20-30) asci are small and narrow. On Quercus the peri- 

 thecia are very large, and the 10-15 asci and the sporidia are much 

 larger than on Ulmus. On Corylus the perithecia are small, but the 

 appendages are very long. It is remarkable for the exceedingly great 

 diversity of the host species which it affects. Scarcely a deciduous 

 leafed tree seems to be proof against it. The most peculiar thing in 

 this connection is its appearance on Typha latifolia (Anderson. Journ. 

 Mycol. V, p. 193). 



In a large number of instances the perithecia have a dense layer 

 of short, branched, fine, hyaline, radiating hyphae, totally distinct from 

 the conspicuously bulbous appendages. There are projections from 

 the wall of the perithecium, issuing from the lower side and forming a 

 .cushion-like mass. 



P0D0SPHJ]RA, Kunze. 



Mycol. Hefte II, p. in. 



Perithecium containing a single ascus. Appendages free from the 

 mycelium, dichotomously branched at the end. 



P. Oxyacanthae, (DC.) (Plate 4) 



Erysiphe Oxyacanthce, DC. Flore Franc. VI, p. 106. 



AlphitomoYpha clandestina, Wallr. Flora Crypt. Germ. Ill, p. 753. 



Erysibe clandestina, Lk. Spec. Plant. VI, I, p. 103. 



Podosphcera Kunzei, clandestina, Lev. Ann. Sci. Nat. Ser. Ill, Tome XV, p. 19. 



Podosphcera minor, Howe, Torr. Bull. V, p. 3. 



Microsphcera fulvo-fulcra, Cke. Grev. VI, p. no. 



Podosphcera Oxyacanthce, DBy. Morph. und Phys. der Pilze, III, p. 480. 



Amphigenous. Mycelium variable, often abundant, persistent. 

 Perithecia 65-110 //, dark, opake, reticulations regular, about 10-15 /i, 

 evident when young, scarcely observable when old, except by the un- 

 even surface ; appendages 8-20, dark brown for more than half their 

 length, frequently septate, 1-4 times as long as the diameter of the 

 perithecium, 3-5 times dichotomously forked, branches short, often 

 swollen, tips, recurved. Ascus broadly elliptical or orbicular, about 

 50 x 60 jul, thick walled. Sporidia usually 8. 



On Prunus domestica, P. Americana, P. Cerasus, P. pumila, 

 P. Virginiana, P. demissa, Spircea salicifolia, S. tomentosa, S. 

 Douglasii var. dumosa, Pyrus Malus, Crataegus Oxyacantha, C. 

 coccinea, C. tomentosa, C. punctata, C. crus-galli, Amelanchier 

 Canadensis, Diospyros Virginiana. 



