THE FUNGI WHICH CAUSE PLANT DISEASE 381 



from a hyphal weft. The fertile branches give rise to chains of 

 spores every alternate cell of which atrophies. The outer row of 

 sporophores and potential spores remains sterile to form the 

 peridium. When young the aecium is immersed and globular, 

 at maturity erumpent and forms an open cup. These spores 

 germinate by a tube capable upon proper hosts of stomatal infec- 

 tion and following this of producing the uredinium. 



Urediniospores are produced throughout the season even through 

 the winter under proper climatic conditions. They also remain 

 viable for weeks ^^' ^'^ and doubtless serve hibernation purposes. '"^ 



Teliospores arise later in the season in the uredinia or in 

 separate telia. Unicellular teliospores, mesospores, are oc- 

 casionally seen. Teliospores germinate best after normal out- 

 door hibernation, producing the tjrpical 4-celled promycelium, 

 long sterigmata and solitary basidiospores. If imder water the 

 usual promycelium becomes abnormal and resembles a germ 

 tube."'- 1" 



The secial stage may not occur under certain climatic conditions, 

 and the uredinia alone perpetuate the ftmgus."^'' ^^^ ^^'' ^ It 

 therefore follows that eradication of the barberry as was at- 

 tempted by legislative enactment in 1660 in Europe and in 1728 

 and 1755 in Coimecticut and Massachusetts ^'^ does not extermi- 

 nate the rust ^^ (see also '"«• ^s). 



Basidiospores were shown by De Bary, ^*^ confirmed by Ward ^^ 

 and Eriksson, to be incapable of infecting wheat leaves. Suf- 

 ficient such attempts have, however, not been made on young 

 tissue. "" 



Jaczewski *^ succeeded in securing germination of pycniospores 

 but the resulting mycelium soon died and infection was not at- 

 tained. The same author holds that aeciospores may remain 

 viable about a month, the urediniospores a much shorter time. 

 • Still hibernation by urediniospores is possible where climatic rela- 

 tions allow the formation of new uredinia during the winter. 



P. rubigo-vera (D. C.) Wint.'"'- '''' '''' "^ 



I (=^. asperifoliimi, Pers). Spots large, generally circular, dis- 

 colored, generally crowded. Peridia flat, broad, with torn white 

 edges. Spores subglobose, verrucose, orange-yellow, 20-25 m- 



II. Uredinia oblong or linear, scattered, yellow, pulverulent. 



