ORNAMENTAL PLANTS 451 



dusty yellow sori upon the lower leaf surfaces. Young trees 

 are sometimes somewhat injured by it, and the trees are 

 rendered unsightly, especially by the defoliation that is 

 induced. In the latter part of the season the winter sori 

 appear as reddish brown to blacjc, waxy or crusty spots. 



A similar rust is conmion upon cottonwood, Balm of 

 Gilead, poplar. 



Powdery mildew. See oak. 



Powdery mildew, uncinulose ( Uncinula Salicis (DC.) 

 Wint.). — A characteristic white flour-like growth appears 

 upon the leaves, usually upon both sides. In later stages 

 small black perithecia are seen upon the white background. 



ORNAMENTAL PLANTS 



VARIEGATED PLANTS, IN GENERAL 



In variegated plants the non-green parts of a leaf afford 

 less resistance to disease than do the green parts of the same 

 leaf. It thus happens that many diseases occur upon the 

 variegated species that are not found upon the usual green 

 species. Variegated Aspidistra, Pelargonium, Alternanthra, 

 Abutelon, Ageratum, Aralia, Begonia, Centaurea, Coleus, 

 Croton, Cyclamen, Dieffenbachia, Dracaena, Euonymus, 

 Ficus, Fraxinus, Funkia, Hedera, Hibiscus, Hydrangea, 

 Impatiens, Maranta, Nepeta, Nerium, Pittosporium, 

 Ptychosperma, Sambucus, Solanum, Sarracenia, Spiraea, 

 Vinca are subject to disease caused by various species of 

 Colletotrichum, Ascochyta, Phyllosticta, Glceosporium, 

 Leptosphaeria, Cercospora, Septoria, Coryneum, Conio- 

 thyrium, Laestadia, and Diplodia. 



