54 BULLETi:^ 957^ U. S. DEPAETMENT OF AGEICTTLTUEE. 



coloration (PL VI, fig. 2). This is most likely to occur on young 

 leaves. It is a fairly certain symptom of a successful inoculation. 



Striking cases of the preservation of the normal green color in the 

 infected areas, while the rest of the leaf is etiolated, have been noted 

 a number of times. 



PALE COLOR OF INFECTED SPOTS' ON THE UPPER SURFACE OF RIBES LEAVES. 



Numerous young Ribes leaves inoculated in the greenhouse devel- 

 oped pale spots on the upper side of the infected leaves (PL V, fig. 1). 

 These varied from nearly white to yellow. Similar spots are often seen 

 in the field. Some species of Ribes seem to be more likely to develop 

 these spots than others. Among those showing this etiolation as a 

 result of infection by Cronartium rihicola may be mentioned: Ribes 

 aureum and its varieties, R. cereum, R. cynosbati, R. divaricatum, R. 

 eryihrocarpum, R. fasciculatum, R. glandulosum, R. Mrtellum, R. 

 inehrians, R. inerme, R. leptanthum, R. nevadense, R. nigrum, R. 

 odoratum, R. reclinatum, R. rotundifolium, R. setosum, R. speciosum, 

 R. triste, and R. vulgare. These spots seem to be produced by condi- 

 tions existing in the immature Ribes leaf when attacked by the 

 fungus very actively. 



REDDENING OF INFECTED SPOTS ON RIBES LEAVES. 



CertaiQ species of Ribes react to infection by Cronartium rihicola 

 by a reddish or purplish coloration around the edges of the infection. 

 This is common with some species, while others apparently must 

 have the leaves at a certain stage of maturity for this coloration to 

 occur, Rihes americanum, R. curvatum, R. rotundifolium, R. vilurni- 

 folium, R. glandulosum (old thick leaves), R. cynosbati (old thick 

 leaves), R. Mrtellum (old thick leaves), R. oxyacardhoides, R. reclina- 

 tum, and R. missouriense develop the red color in the order named. 



DEAD AREAS OF INFECTED LEAP TISSUE, 



Where the attack of Cronartium ribicola is intense, areas of the 

 oldest infected tissue of the diseased leaves collapse and die (PL V, 

 figs. 3 and 4 ; PL VI, fig. 3) . The different species of Ribes vary much 

 in this respect, some developing dead spots very quickly and some 

 doing so only after considerable time, Ribes nigrum usually resists 

 death tenaciously. When a spot dies it is commonly a large one and 

 soon results in the premature fall of the affected leaf. At the other 

 extreme is R. leptantJium. With this species the infected spots die 

 very quickly, even before m-edinia can form (147). Less than 10 per 

 cent of these spots produce any uredinia or telia, and those few spots 

 bearing sori usually have only from one to several stunted sori. All 

 species of Ribes tested have sooner or later developed dead spots. 

 Just how much secondary fungi contribute to the kdling of host 

 tissues is entirely unknown. 



