WHITE-PIXE BLISTER EUST. 49 



SORI ox COTYLEDONS. 



The cotyledons of young Ribes seedlings are apparently quite sus- 

 ceptible to infection by geciospores and urediniospores of Cronartium 

 ribicola. Relatively heavy infection has resulted from inoculations 

 on the lower surface of cotyledons of Rihes americanum, R. missouri- 

 ense, R. oiyacanthoidor., R. rotundi folium, R. glandnlosum, and R. 

 fasciculatum seedlings in the greenhouse and on R. glandulosum in the 

 field. 



SORI OX FLORAL BRACTS AXD BUD SCALES. 

 \ 



Infection was secured by Gravatt from inoculations of the floral 

 bracts of Rihes aureum in several different cases in the greenhouse. 



Infection of opening buds and of bud scales merits more investiga- 

 tion. McCubbin (85) suggested the possibility of infection of partially 

 open buds in the fall and the overwintering of the fungus, but he 

 could not prove that it occurs. Infection of young leaves scarcely 

 out of the bud occurs, but it seems to be limited to leaves that are 

 relatively mature, though small. (See discussion on pp. 44 to 46.) 

 Search for infections of buds on heavily infected Rihes nigrum bushes 

 failed to reveal any infections (151, p. 44). Gravatt made inoculations 

 of buds about to open, but with no success. York-*' has inoculated 

 successfully an inner bud scale of Rihes nigrum. 



SORI ox PETIOLES. 



Next in frequency to infection of the lower surface of the leaf 

 blade is infection of petioles. The first published account of tliis, 

 so far as the writer knows, was given in 1912 (133, 134, 135) and 1913. 

 At that time it was considered to be very uncommon. Since than 

 a considerable number of such cases have been noted both in the 

 greenhouse and out of doors. The following species have developed 

 uredinia or telia, or both, upon petioles, as many as 25 or more 

 petioles on a single plant being thus attacked: Rihes americanum, 

 R. aureum, R. hracteosum, R. cereum, R. culverwellii, R. cynoshati, 

 R. divaricatum, R. erythrocarpum, R. fasciculatum, R. giraldii, R. 

 glandulosum, R. inerme, R. lacustre, R. nevadense, R. nigrum, R. 

 parishii, R. petraeum, R. rohustum, R. setosum. The follo^ving 

 cultivated varieties have had petiolar attacks: Rihes nigrum hort. 

 vars. Black Victoria, Climax, and Seabrook Black; R. reclinatum 

 hort. vars. Berkeley, Golden Prolific, Poorman, Transparent, and 

 Van Fleet; R. vulgare hort. var. White Imperial. Some 10 or 12 

 as yet unidentified species collected by Beattie in the Rocky Mountain 

 and Pacific coast regions have exhibited the same phenomenon. 



soyork, H.H. Op.cit. 



40103"— 21— Bull. 9ri7 4 



