i2 Bulletin 313 



Rhysotheca potentill^ de Bar>'. — On the under surface of the 

 leaves of Potentilla. Causes spots bounded by the veins which are 

 yellow above and smoky below. Conidiophores in tufts, 5-6 times 

 dichotomously branched, branches moderately elongated, tips 

 bluntly pointed, conidia ellipsoid, obtuse, smoky-colored, oospores, 

 20-26x 15-19 /i; oospores spherical, yellow, smooth, 22-24 /i, in di- 

 ameter. 



Z7. Conidiophores and conidia, 1/12, 



Rhysotheca viburni (Peck) Wilson. — On leaves of Viburnum 

 lanfana. Causes irregular spots with various sizes on margins or 

 along larger veins, covered on under surface with sparing white 

 downy growth. Spot discolorations ranging none to dark reddish- 

 brown or chocolate color. Conidiophores clustered, 300-600 x 6-8 ju,, 

 2-4 branched, last branchlets 6-8. Conidia elliptical, sometimes glo- 

 bose, 15-30 yi 12-1 5 fi. 



38. Conidiophores and conidia, 1/12. 



Rhysotheca viticola* (B. & C.) Wilson. — On leaves, stems and 

 sometimes on fruits of both wild and cultivated grapes. Causes 

 spots of various sizes and forms on leaves, yellowish on upper and 

 whitish on lower surface, becoming brown with age. Dr. B. D. 

 Halsted also reports it on Parthenocissus tricuspidata (N. Am. 

 Fungi, 2427 b, on "Ampelopsis ritchii/' error for horticultural name 

 of A. veitchii.) Diseased fruit rot. The affected surface of the 

 stem and fruit and under surface of leaf covered with a vv^hite 

 downy growth of aerial hyphae which become brown. Conidio- 

 phores arise from stomata in clusters, 250-850 x 5-8 ju,. 4 or 5 times 

 branched, the last branches about 8. Conidia elliptic-ovate. 

 9-12 X 12-30 /i. 



Very common in vineyards. 



39. Infected grape leaf. 40. Conidiophores and conidia, 1/12. 



*Plasmopora viticola. 



