1 66 Journal of Agricultural Research voi. xxn. no. 3 



were present in the aecial material on Thalictrum which he used for the 

 culture. A study of the aecia used in these cultures shows the dimensions 

 of the peridial cells to be 15 to 19 by 23 to 29 n with the outer wall 7 to 

 10 /x and the inner 3 fx thick and the aeciospores 14 to 19 by 19 to 23 p. in 

 diameter. 



A comparison of the foregoing description of the aecia of Puccinia 

 triticina with the measurements given for the various grass rust aecia on 

 Thalictrum shows surprisingly little variation. The aecia of P. Cockerel- 

 liana show the greatest difference, having larger peridial cells and some- 

 what larger aeciospores with much thicker walls than the aecia of P. triti- 

 cina. Slightly smaller aeciospores occur in P. horealis and P. obliterata, 

 and the aecial infection causes little or no hypertrophy of the host. 

 The remaining aecia differ mainly in slightly thicker walls of the peridial 

 cells. 



It is evident that Puccinia triticina is closely related to P. persistens. 

 Whether the name Aecidium Tlialictri-flavi (DC.) Wint. should apply to 

 the aecial stage of the former is a question which can not be answered 

 with the available information. De Candolle (7, p. giy) described 

 A. Ranunculacearum for aecia occurring on the family Ranunculaceae 

 and as a variety of this gives Thalictri-flavi without further description. 

 Winter (24, p. 269) raises this variety to specific rank and gives a 

 description which, however, could apply to the aecia of either rust. 

 As both P. triticina and P. persist-ens are common rusts throughout 

 Europe, there is no way of determining definitely to what aecia the name 

 was applied beyond the fact that they were on Thalictrum flavum. As 

 it has been shown that at least some aecia on that host in England belong 

 to P. persistens the name A. Thalictri-flavi should be retained for the 

 present as a synonym of that species, at least until aecia can be found 

 in Europe upon T. flavum which will produce the leafrust of wheat. 



Upon their grass hosts these rusts present a somewhat greater varia- 

 tion. They all have uredinia with globoid or ellipsoid urediniospores 

 with a varying number of scattered pores, usually more than six, and 

 with few or no paraphyses. The telia are long, covered by the epidermis, 

 usually with more or less stroma present, and the teliospores are cylindric, 

 more or less flattened at the apex, and with a very short pedicel. Puc- 

 cinia Cockerelliana differs most noticeably from P. triticina in that the 

 teliospores are much longer and the telia do not remain entirely covered 

 by the epidermis at maturity. P. Elymi differs especially in the thicker 

 and darker walls of the urediniospore and in the longer teliospores which 

 are often many-celled. P. alternans, P. borealis, P. obliterata, and P. 

 persistens differ but little, mostly in the tinting of the urediniospore wall 

 and a slight variation in pore number. 



Although the morphological differences between Puccinia triticina and 

 the related rusts discussed above are not great, their biologic specializa- 



