374 BROOKLYN BOTANIC GARDEN MEMOIRS 



Uromyces Pisi (Pers.) Winter. This rust is heteroecious forming 

 its aecidial stage on various species of Euphorbia and its uredo and 

 teleuto stages on species of Lathy r us and Pisum. The aecidial my- 

 ceHum is perennial in the Euphorbia host. It may also be noted that 

 aecidial stages on Euphorbia, especially E. cyparissias, have been 

 connected with a number of different species of Uromyces on legumes. 

 The aecidia belonging to these different rusts are quite indistinguish- 

 able by structural features. Jordi (70, 71) suggests that specialized 

 races of U. Pisi occur on Lathyrus pratensis and Vicia cracca; the 

 latter race is by some recognized as a species — Uromyces Fischeri- 

 Eduardi. 



Uromyces proeminens (DC.) Lev. P. and H. Sydow (151) list 

 twenty-eight species of Uromyces on the species of Euphorbia, basing 

 their separations largely on the studies of Tranzschel (157) in this 

 group of rusts. Nine species are recorded as autoecious and have all 

 four spore-forms present, the others either being short-cycled or the 

 life history incompletely known. The structural differences between 

 many of these species are very slight and the characters used as a basis 

 for separation are, in many cases, quite variable. In fact Arthur (12) 

 has grouped several of the full-cycled forms under the one species 

 Nigredo proeminens, suggesting the occurrence of specialized races. 

 Arthur (i, 2, 3) has obtained the following results with inoculation 

 experiments: aecidiospores from Euphorbia nutans infected E. nutans 

 but not E. maculata, E. marginata nor E. humistrata; aecidiospores 

 from, E. humistrata ififected E. humistrata and E. nutans but not 

 E. maculata; uredospores from E. dentata infected E. dentata but not 

 E. humistrata, E. nutans nor E. marginata; uredospores from E. nutans 

 infected E. nutans but not E. maculata. 



Arthur (12) suggests that a race is restricted to the section Poin- 

 settia, a second race to the section Dichrophyllum, a third race to the 

 prostrate species, and the fourth to the more upright species of the 

 section Chamaesyce of the genus Euphorbia. 



Uromyces Scirpi (Cast.) Burr. This rust has its uredo and teleuto 

 stages on Scirpus maritimiis and its aecidial stage on Glaux maritima, 

 Hippuris vulgaris, Berula angustifolia, Daucus carota, Oenanthes 

 aquatica, 0. crocata, Pastinaca sativa and Sium latifolium in Europe. 

 The similar rust in this country forms its uredo and teleuto stages on 

 Scirpus americanus, S. campestris, S. fluviatilis and 5. robustus, and 

 its aecidial stage on Cicuta bulbifera, C. maculata, Glaux maritima, 

 Oenanthes Californica and Sitim cicutaefoUum. A good deal of experi- 

 mentation has been carried on by Klebahn and others to determine the 

 host relations of the rust and various races have been separated out 

 as distinct species. Klebahn (89, 91) distinguishes the following: 



