I8d9j MICROSCOPICAL JOURNAL 173 



Uncinula salicis (DC.) Winter. Figs. 10, 17, 18 

 (perithecium, ascus, ascospores). 



Phyllactinia suj^ulta (Reh.)S&cc. Fig, 11 (perithecium, 

 ascus, ascospores), 



Microsphaera alni (DC.) Winter. Figs. 12, 14, 15 

 (perithecium, ascus, ascospore). 



Podosphaera oxycanthae (DC.) DeB. Fig. 13 (perithe- 

 cium). 



Organs Exhibited. 



Peritiiaecium. — The six prominent objects (fig. 7, 

 Erysiphe ; fig. 9, Sphaerotheca ; fig. 10, Uncinula; fig. 

 11, Phyllactinia ; fig. 12, Microsphfera ; fig. 13, Podo- 

 uphaera) all with round bodies having different kinds of 

 appendages are perithecia of diflFerent species, and in- 

 side of each perithecium are one or more asci (shown in 

 figs. 8, 14, 16, 17). In Sphaerotheca (fig. 9), and Podo- 

 sphaera (fig. 13) is only one ascus ; bnt in Erysiphe (fig. 7) 

 and Microsphaera (fig. 12) there are several asci. 



Appendages of the Perithecia. — Those of Sphaero- 

 theca (fig. 9) and Erysiphe (fig. 7) are similar to myce- 

 lium (see fig. 1) but they differ in the number of asci 

 contained within. Those of Uncinula (fig. 10) are coiled 

 at the tips ; those of Phyllactinia (fig. 11) are swollen at 

 the base ; those of Microsphaera (fig. 12) and those of 

 Podosphaera (fig. 13) are both branched at the tips but 

 they differ in the number of asci borne within. Thus 

 the perithecia furnish means of distinguishing these six 

 genera. 



Ascus. — One in each perithecium, Sphaerotheca (fig. 

 16) and Podosphaera. Several in each perithecium, Ery- 

 siphe (fig. 8), Microsphaera (tig. 14), Uncinula (fig. 17) 

 and Phyllactinia. 



Ascospores. — Microsphaera (fig. 15), Uncinula (fig. 18). 



Collecting will naturally be easier as the season pro- 

 gresses so that by August or September many kinds of 

 mildews can be seen readily. The collected leaves can 



