EXPEKIMEXT S'lATlON JMOl'Oin'. 531 



The winter s])()iv> tluit form after tlie mildew has vegetated for 

 ii lime are (juite ri'e(|iu'iitly upon tlie uiult-r side of the leaf, and in 

 many instances only found then. Plate XII., Fig. 4, shows the under 

 side of a leaf of garden phlox. u])on whieh, as the leaves are ready to 

 fall, the peritheeia are in ahundaiu-e, and may Ije seen as small, dark 

 specks, the indistinctness l)eing i)artly due to the surrounding hrown 

 threads that partially envelop the spore-cases. Sometimes the peri- 

 theeia entirely coat over the surface of the leaf, and, as each of these 

 cases contains many spores, it is no wonder that the mildew is kept 

 over the winter and is ready to begin life anew when another season, 

 -with, fresh foliage, is at hand. 



An under side of a lilac leaf is shown at Fig. 3. This leaf was 

 gathered some weeks later than the one shown in Fig. 1, and after 

 the under surface had become evenly coated with the mihU'W threads 

 and upon which the dark spore-caf>es formed. In tlu' lilae the 

 peritheeia are less enveloped l)y brown threads and the minute dark 

 spots are therefore more e\idcnt. Unfortunately the leaf is reduced 

 below natural size, or else the jieritheci;! containing the winter spores 

 would be more clearly seen. 



Below is given a ])reliminary list of the s])ecies of powdery mildews 

 of cultivated })lants. with the leading hosts under each. Following 

 each host name is given the abhreviations of the States in which the 

 plant has bwn recorded with the mildew upon it. The list of papers 

 consulted follows at the close of this article. 



I. PoDOSPH-iERA. Kunze (1823). 



1. Podosphara Oxyacanthce (DC), De Bary. 



Erysiphe Oxycantha? DC. (1807), as above, 1870. 

 Pomacejp, Crata?gus Sp. — W. Va., Ind., Ill , Ala., Can. 

 Pomacea?, Malus Malus (L.)— Vt., Mo., Ala. 

 Pomacea?, Pyrus Cydonia L. — Ind. 

 Drupaceaj, Prunus Cerasus L. — N. Y., N. J., O., Ind., 111., Ala., Neb., Kan. 



2. Podosphcera leucotricha (E. & E.) Salm. 



Sparotheca leucotricha E, & E., 1888, as above, 1900. 

 Pomacese, Malus Malus (L.) — Vt., Mo. 



II. SpHiEROTHECA. LcveUle (1S51). 



3. Sphcerolheca Humuli (DC.) Burr. 



Mucor Erysiphe Linn (1753). Erysiphe humuli DC. (1815), as above (1887). 

 Moracefe, Humulus Lupulus L. — Ala , Wyo., Cal. 



4. Sphcerolheca Humuli (DC.) Burr, var fuliginea (Schlecht) Salm. 



Alphitomorplia fuliginea Schlecht, 1819, as above, 1900. 

 Bosacese, Fragaria cult. — N. Y. 



