REED: SPECIALIZATION OF PARASITIC FUNGI 369 



and also uredospores produced by aecidiosporic inoculations were 

 also used. As the result of the experiments, Jacob concludes that the 

 rusts on Polygonum amphibium and on P. convohndus and P. dume- 

 torum are distinct. The relationship of these two forms may be 

 indicated as follows: 



1. Puccinia Polygoni-amphihii Pers.; aecidial stage on Geranium 



albannm, G. columhinum, G. dissectiim, G. lucidum, G. molle, 

 G. nodosum, G. pratense, G. pusillum, G. pyrenaicum, G. rivulare, 

 G. rotundifolium and G. sanguineum; uredo and teleuto stages 

 on Polygonum amphibium. 



2. Puccinia Polygoni Alb. et Schw. (P. Polygoni-Convolvuli DC); 



aecidial stage on Geranium columbinum, G. dissectum, G. molle, 



G. pusillum, and G. rotundifolium; uredo and teleuto stages on 



Polygonum convolvulus and P. dumetorum. 



It may be noted that the same species of Geranium occur as hosts 



for both races, although the host list for Puccinia Polygoni-amphibii 



includes more species than the other. 



Puccinia absinthii DC. Klebahn (91) suggests the probability of 

 specialized races in this rust although no cultural experiments have 

 been carried out. He reports, however, minute differences in the spore 

 measurements of the different forms. The following races are indicated : 



1. Absinthii on Artemisia absinthium. 



2. Artemisiae on Artemisia vulgaris. 



3. Abrotani on Artemisia abrotanum. 



Puccinia buUata (Pers.) Winter. This rust, according to Semadeni 

 (i35) 136), has a race specialized to Silaus pratensis and one to Thys- 

 selinum palustre. 



Puccinia carduorum Jacky. Probst (112) recognizes three special- 

 ized races in this rust. 



1. Crispi on Carduus crispus and C. personata. 



2. Deflorati on Carduus defloratus. 



3. A third race probably occurs on Carduus nutans. 



Puccinia Centaurea Mart. Jacky (64) and Hasler (62) have both 

 studied the specialization of this rust. Jacky suggested the occurrence 

 of two specialized races: (a) Jaceae on Centaurea Jacea and (&) Ner- 

 vosae on C. nervosa. Hasler separates out three rusts, making them 

 species and finds additional host specialization in one of these. His 

 arrangement is as follows: 



1. Puccinia Centaureae-vallesiacae Hasler on Centaurea vallesiaca, C. 



alba, C. rhenana and, to a less extent, on C. cyanus. 



2. Puccinia Jaceae Otth on Centaurea Jacea, C. rhenana and, to a less 



extent, on Centaurea austriaca, C. Jacea var. longifolia, C. 

 phrygia and C. transalpina. 



