82 THE FUNGI WHICH CAUSE PLANT DISEASE 



unequally curved at base, 15 x 30 /x; conidia hyaline; short- 

 cylindric, all alike or the terminal more rounded, 14-20 x 12-18 fi; 

 the membrane with an equatorial thickening, usually very pro- 

 nounced. Oosporic sori separate from the conidial, caulicolous, 

 rarely on petioles, 1-2 x 5-6 cm. or even more, causing marked 

 distortion; oospores light yellowish-brown, 25-55 n; epispore 

 papillate or with irregular, curved ridges. 



Conunon throughout the world on various species of Convol- 

 vulacese, morning glory, moon flower, sweet potato, etc., although 

 causing but little damage. 



A. occidentalis G. W. W., reported by Pammel ^ on the beet 

 has been collected but once. 



A. portulaceae (D. C.) Kze. on purslane *^ and A. bliti (Biv.) 

 Kze.^^ occur on Amaranthus and related plants. 



A. tragopogonis (D. C.) S. F. G."- " Sori hypophyllous or 

 cauhcolous, prominent, deep-seated, white or yellowish, pul- 

 verulent, rounded or elongate, 1-3 x 1-8 mm; conidiophores 

 hyalme, clavate, about 12-15 x 40-50 n; conidia, 12-15 x 18-22 ft; 

 light yellow or hyaline, short-cylindric, the terminal larger and 

 less angular than the others, membrane with an equatorial thick- 

 ening; oospores produced in stems and leaves, dark brown or 

 almost black at maturity, opaque, 44-68 /i, epispore reticulate, 

 areolae 2 ju; wing bearing papillate tubercles at its angles. 



A cosmopoUtan species of less economic importance in America 

 than in Europe attacking a wide range of hosts of the Compositse. 

 Salsify is the chief economic host. 



Peronosporacese (p. 78) 

 The members of this family, producing the diseases commonly 

 known as the "downy mildews," have been long known and much 

 studied. They contain many important plant pathogens. The 

 globular oospores are in general indistinguishable from those of 

 the Albuginaceae but the conidiophores are quite different from 

 those of that family, being aerial instead of subepidemal. In 

 most cases they are branching and tree-like. Fig. 63, but in a 

 few genera they are short. The oospore in such genera as have 

 been studied (Peronospora '' Sclerospora ") is formed as in Albugo 

 resultmg when mature in an uninucleate egg surrounded by a 



