Physiologie. — Pflanzenkrankheiten. 213 



Das Längenwachstumsmaximum liegt überhalb 40°; in lang- 

 andauernden Versuchen etwas niedriger. Ob es eine Sachs'sche 

 Wärmestarre gibt, lässt sich nicht aussagen; die beobachtete 

 Wachstumsgeschwindigkeit bei 37—38° C ist gleich; vielleicht findet 

 also nach 31/0 Stunde kein Wachstum mehr statt. Der Kurvenverlauf 

 weist aber hin auf eine mögliche Analogie zwischen Minimum und 

 Maximum, wenn eine sehr genaue Beobachtungweise ermöchlicht 

 werden kann. M. J. Sirks (Wageningen). 



Stakman, E. C. and F. J. Piemeisel. ■ Biologie forms of 

 Piiccinia graminis on cereals and grasses. (Journ. agric. 

 Research. X. p. 429—495. 1917.) 



The writers have collected Puccinia graminis on about 35 

 species of grasses in the Upper Mississippi Valley, a part of the 

 Northern Great Plains region and a small area of the Pacific 

 Northwest. 



Inoculation experiments with the rust from about 30 grasses 

 were made and the following biologic forms were isolated: Pucci- 

 nia gratninis tritici, P. g. tritici conipacti, P. g. secaliSj P. g. avenae, 

 P. g. phleipratensis and P. g. agrostis. Of these P. g. tritici conipacti 

 was found only in the Palouse country of Washington and 

 Idaho; it occurs on club wheat and grasses which, east of the 

 Rocky Mountains, are hosts for P. g. tritici. No ordinary P. g. 

 tritici was found west of the Rocky Mountains. 



More than one biologic form may occur on the same host in 

 nature, sometimes even on the same plant. In such cases it is 

 necessar}'- to employ differential hosts to determine the identity of 

 the forms. P. g. tritici and P. g. secalis have been found associated 

 most often. 



Different strains of the same biologic form sometimes differ in 

 virulence on the hosts; but the differences are usually in degreeonly. 



There seems to be no sharp geographical specialization of 

 biologic forms in the upper Mississippi Valley and Northern 

 Great Plains area, where the biologic forms are quite uniform. 



On the basis of parasitism the biologic forms can be divided 

 into two groups: one containing P. g. tritici, P. g. tritici conipacti, 

 and P. g. secalis, the other P. g. averiae, P. g. phleipratensis, 

 and P. g. secalis. 



Wheat, club wheat, rye and Agropyron repens, are differential 

 hosts for group 1. The tritici form infects wheat and club wheat 

 readily and rye and A. repens weakly; the secalis form develops 

 normally on rye and A. repens, but very rarely attacks the other 

 two. All three develop well on barley, Hystrix patula, and Brorniis 

 tectoruni and on a number of species of Agropyron, Elymus and 

 Hordeinn. 



Differential hosts for the forms of group 2 are oats, Phleum 

 pratense, and Agrostis spp. The avenae form develops normally on 

 oats, infects Phleum pratense weakly, and develops fairly well on 

 Agrostis alha\ the phleipratensis form grows normally on Phleum 

 pratense, infects oats rather weakly and has not yet infected 

 Agrostis alba] the agrostis form develops normally on Agrostis 

 spp., infects oats very weakly, and has not yet infected Phleum 

 pratense. All three infect barley and rye weakly, but develop 

 well on Koeleria cristata, Holcus lanatus, Dactylis glomerata, 

 Alopecurus geniculatus and A. pratensis. 



