32 Bulletin 313 



Sph^rotheca humili var. fuliginea (Schl.) Sal. (= Oidium 

 fragariae, page 116). — On flowers, leaves and stems of hops.* 

 Causes circular, white, powdery spots which enlarge and unite, 

 forming large irregular areas. Most severe on the young tender 

 parts. White downy growth disappears with age leaving brown 

 spots. The perithecia are formed in these brown areas. Perithecia 

 not more than .50 /x in diameter, appendages short and light brown. 

 Asci broadly elliptic to sub-globose and containing 8 spores each. 

 Ascospores 20-25 x 12-18 /x. 



113. Conidiophore and spores, 1/6. 114. Conidia, 1/12. 115. Perithecia, 

 1/6. 116. Ascus, 1/12. 117. Ascopores, 1/12, 



Sph^ROTHEca pannosa (Wal.) Lev. (= Oidium leucoconium 

 Desm., page 116). — On the green parts of roses and peaches. Causes 

 a stunting of young growths and prevents normal development of 

 the flower. Affected parts are covered with a dense satiny growth 

 of mycelium which is more persistent than S. humili, shiny white, 

 finally becomes gray, buff or brownish. Conidia ovoid hyaline, 

 20-30 X 13-16 fji, and borne on short conidiophores. Perithecia sur- 

 rounded by mass of mycelium. Appendages few, sometimes obso- 

 lete, very short tortuose, pale brown, septate globose to pyriform, 

 and about 85-120 (usually 100) fi. Asci broadly-oblong to almost 

 spherical, 88-115 ix, averaging 100 x 60-75 fi. Ascospores 20-27 x 

 12-15 fx. Conidia common on rose but perithecia are rare. 



lis. Conidiophores 1/6. 119. Spores, 1/12. 120. Perithecium, 1/6. 121. 

 Ascus, 1/12. 122. Ascospore, 1/12. 



Uncinula necator (Schw.) Burr. (= Oidium tuckeri Berk., 

 page 116). — On the young leaves, young shoots and fruits of grape, 

 ampelopsis, etc. Produces a luxuriant, persistent growth of my- 

 celium. Conidia elliptic, oblong or obtusely rounded, hyaline, 25-30 

 X 15-17 fjL. Perithecia on both leaves and fruit more or less scat- 

 tered, 70-128/1; appendages septate, 7 to 30 and rarely 40 in length; 



*Also on strawberry, dandelion and other hosts. 



