164 Journal of Agricultural Research voi. xxii. no. 3 



Aecia hypophyllous, crowded in more or less swollen, gall-like, reddish 

 brown or yellowish areas 2 to 15 mm. in diameter, cupulate or short 

 cylindric, 0.2 to 0.6 mm. in diameter, up to 0.5 mm. high; peridium white 

 or yellowish, the margin erose or somewhat lacerate, recurved; peridial 

 cells oblong or somewhat rhomboidal in longitudinal radial section, 14 to 

 19 by 18 to 29 IX, abutted or slightly overlapping, the outer wall 6 to 7 /x 

 thick, transversely striate, the inner wall thinner 2 to 3 yLt, very coarsely 

 verrucose; aeciospores angularly globoid or ellipsoid, 16 to 20 by 16 to 

 26 /x; wall colorless, thin, i /i or less, very closely and finely verrucose. 



The pycnia and aecia usually were produced in definite galls or swellings. 

 These galls apparently were formed by the excessive enlargement of the 

 cells of the infected areas, especially those of the mesophyll. When 

 infection took place in the young, rapidly developing tissue of the petiole, 

 galls developed (PI. 21, D) which were 10 or 15 times as large as the 

 normal petiole. A very noticeable odor, resembling that of the hyacinth, 

 was often detected as the pycnia reached maturity. 



GENERAL DISCUSSION OF RESULTS 



The discovery that species of Thalictrum are the aecial hosts for 

 Puccinia triticina goes to support Arthur's contention {i, v. 9, p. 304) that 

 the leafrust of wheat is closely related to grass rusts of the type of Puccinia 

 Agropyri, having aecia on species of the family Ranunculaceae. A num- 

 ber of cultures have been made with rusts of this type, connecting them 

 with various species of Thalictrum. Plowright, in England {21, p. j8i), 

 connected aecia on Thalictrum flavum with a rust on Agropyron repens. 

 To this rust he gave the name Puccinia persistens Plowr. He considered 

 Aecidium Ranunculacearum 7 Thalictri flavi DC, and Aecidium Thalictri 

 fiavi (DC.) Winter as synonyms, and describes the aecia as occurring 

 on thickened spots with aeciospores subglobose 17 to 20 by 20 to 30 /i. 

 Fischer (12, p. 37-63), in Switzerland, cultured a rust from Poa nemoralis 

 var. firmula on Thalictrmn minus, T. aquilegijolium and T. foetidum. 

 On account of the morphological similarity, he concluded that his material 

 belonged to Puccinia persistens, although he made no cultures on either 

 Agropyron repens or T. flavum. He describes the aecia (ij, p. 347-349) 

 as having peridial cells with the outer wall 4.5 to 13.5 ^ thick and the inner 

 2 to 6 fjL and aeciospores 10 to 21 /x broad and up to 28 /i long. An exam- 

 ination of Sydow's Uredineen No. 725, issued as Puccinia persistens on T. 

 aquilegifolium, shows the following measurements : Peridial cells, 18 to 23 

 by 21 to 26 /x; outer wall, 7 to g fx; inner, 3 to 5 /x; aeciospores, 16 to 19 

 by 19 to 26 n. 



Juel (j<5, p. 411), in Sweden, made cultures connecting aecia on Thalic- 

 trum alpinum with a rust on Agrostis borealis and Anthoxanthum odor- 

 atum. To this rust he gave the name Puccinia borealis Juel, and con- 

 sidered Aecidium thalictri Grev. as a synonym. His description follows: 

 Pycnia not present; aecia not causing hypertrophy of host tissue; aecio- 



