52 BULLETIN 957, U. S. DEPAETMENT OF AGRICULTUKE. 



DISTRIBUTION AKD SIZE OF THE SOEI AND COLONIES. 



It has been found that Cronartium rihicola forms its uredinia and 

 telia upon each species of Ribes in a manner which in general is 

 characteristic of that host species (Pis. IV; 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- 

 mellae, 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.^^ — 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. petroivalskyanum., 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 vulgar e: Sori not plentiful, clustered on spots; spots small and isolated 

 (PI. IV, fig. 3; V. fig. 4). 

 Heritibra. — 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. 1). 



Ribes erythrocarpum: Sori plentiful, clustered. 

 Calobotrya. — Ribes glutinosum: Sori thickly clustered in local areas. 



Ribes nevadense: Sori thickly grouped on local spots; spots large and distinct. 



Ribes viscosissimum: Sori isolated, scattered over entire leaf surface. 

 Symphocalyx. — Ribes aureum and vars. tenuiflorum 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; fasciculatuvi, "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. 



33 The species of Ribes are grouped according to the arrangement of Janczewski (60). 



