52 BULLETIN 957, IT. S. DEPARTMENT OF AGRICULTURE. 
DISTRIBUTION AND SIZE OF THE SORI AND COLONIES. 
It has been found that Cronartium ribicola forms its uredinia and 
telia upon each species of Ribes in a manner which in general is 
characteristic of that host species (Pls.IY; V. figs. 1, 3. and 4: and VI). 
This was noted in 1902 by Hennings (52, 53), who described some of 
the more striking variations. Like all general statements, the fol- 
lowing are subject to individual variations from the normal or average 
condition for the host species. A statement by Hennings (52, p. 130) 
indicates the degree of variation discernible to a keen observer: 
- It is especially noticeable that the fungus, according to the character of the leaves 
of various species of Ribes, shows great variations in the form and color of the spots 
produced on the leaves, the form and size of the sori, and the size of the telial colu- 
mella, so that a new observer would assume that several of the fungus forms were 
specifically distinct. 
In general, on species which are closely related, or which closely 
resemble each other, the fungus behaves in a similar manner. Some 
of the more striking variations are described as follows: 
Ribesia. 33 — Ribes petraeum and var. atropurpureum: Sori close together and evenly 
distributed over the spots; spots large, soon overrunning a large part of the leaf 
surface. 
Ribes rubrum vars. petroualskyanum, pubescens, and sibirica: Very scant 
sori, located beside large veins of leaf: var. scandicum has abundant sori, close 
together, generally distributed. 
Ribes triste: Sori clustered on definite spots; spots small, widely separated. 
Ribes vulgare: Sori not plentiful, clustered on spots; spots small and isolated 
(PI. IV, fig. 3; V. fig. 4). 
Heritiera. — Ribes coloradense: Sori thickly clustered on diffuse spots. 
Ribes glandulosum: Sori usually thinly scattered over large diffuse spots or 
entire leaf surface, telia very slender and long (PI. VI, fig. i). 
Ribes erythrocarpum: Sori plentiful, clustered. 
Calobotrya. — Ribes glutinosum: Sori thickly clustered in local areas. 
Ribes netadense: Sori thickly grouped on local spots: spots large and distinct. 
Ribes xiscosissimum: Sori isolated, scattered over entire leaf surface. 
Symphocalyx. — Ribes aureum and vars. tenuifiorum and palmatum: Sori abundant, 
closely grouped in rather distinct spots which usually are well separated from 
each other (PI. IV, fig. 1). 
Ribes odoratum: Sori abundant, closely grouped in spots usually well sepa- 
rated from each other. 
Arophyllum. — Ribes cereum: Sori clustered on definite rounded spots which soon 
die. 
Ribes inebrians: Sori on rounded spots. 
Eucoreosma. — Ribes americanum: Sori sparse and scattered, on small irregular spots 
which redden and die: heavy infection rare; telia short, one-half to 1 mm. 
Ribes bracteosum: Sori plentiful, on large diffused spots or patches of leaf 
surface. 
Ribes nigrum (PI. IV, fig. 4) and vars. aconitifolium, fasciculatum, " folio 
argentea": Sori crowded densely, often over entire leaf surface, vigorous; telia 
abundant, reaching 2 mm. in length. 
Ribes viburnifolium: Sori scant, dead spots form early. 
» The species of Ribes are grouped according to the arrangement of Janczewski (60). 
