54 BULLETIN 957, U. S. DEPARTMENT OE AGRICULTURE. 
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 OP INPECTED SPOTS OX THE UPPER SURFACE OP PIPES LEAVES. 
Numerous young Bibes 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 ribicola may be mentioned: Ribes 
aureum and its varieties, R. cereum, R. cynosbati, R. divaricatum, R. 
erythrocarpum, R. fasciculatum, R. glandulosum, R. hirtellum, R. 
inebrious, 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 OP INFECTED SPOTS ON RIBES LEAVES. 
Certain species of Ribes react to infection by Cronartium ribicola 
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. Ribes americanum, R. curvatum, R. rotundifolium, R. viburni- 
folium, R. glandulosum (old thick leaves), R. cynosbati (old thick 
leaves), R. hirtellum (old thick leaves), R. oxyacanthoides , R, reclina- 
tum, and R. missouriense develop the red color in the order named. 
DEAD AREAS OP 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 com m only a large one and 
soon results in the premature fall of the affected leaf. At the other 
extreme is R. leptanthum. With this species the infected spots die 
very quickly, even before uredinia 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 killing of host 
tissues is entirelv unknown. 
