MILDEWS AND RELATED FUNGI 



157 



spJuera (Fig. 54) dichotomously branched. These appendages prob- 

 ably assist in the distribution of the perithecium, serving to attach 

 the perithecia to plants, if wind-borne, or to the bodies of insects by 

 which they are carried to other plants. The number of asci found in a 

 perithecium and the number and character of the spores in the asci 

 vary generically (see Appendix VIII, pages 721-726). 



As the fungi of this family are especially suitable for systematic 

 study, a key is given not only of the principal genera, but also of the 



Fig. 54. — Lilac mildew, Microsphcera alni. A, Perithecium with appendages; 

 B, perithecia showing ascj (a); C, ascus with ascospores; D, conidiophore (fph), 

 bearing conidiospores (c.s.); E, beginning of fertilization; anth, antheridium;. car, 

 carpogonium; F, later stage of fertilization showing the fusion of two nuclei (J). 

 (From Gager with E and F after R. A. Harper.) 



principal species of the different genera. These keys (p. 721) have been 

 taken from a monograph of the Erysiphace^ by Ernest S. Salmon, pub- 

 Hshed in 1900, as vol. ix of the Memoirs of the Torrey Botanical Club, to 

 which the mycologic student is referred for detailed descriptions of the 

 various species. The material for the systematic study is easily kept 

 in the dry condition and the perithecium can be studied in situ on the 

 dried leaf or other plant parts, and later treated with weak alcohol 



