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 Lathyrus and Pisum. The aecidial my- 
celium 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- 
Eduard. 
Uromyces proeminens (DC.) Lév. 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 (1, 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 infected E. humistrata and E. nutans but not 
E. maculata; uredospores from EF. dentata infected E. dentata but not 
E. humistrata, E. nutans nor E. marginata; uredospores from E. nutans 
infected E. nutans but not FE. 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 maritimus and its aecidial stage on Glaux maritima, 
HMippuris vulgaris, Berula angustifolia, Daucus carota, Oenanthes 
aquatica, O. 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 S. robustus, and 
its aecidial stage on Cicuta bulbifera, C. maculata, Glaux maritima, 
Oenanthes Californica and Sium cicutaefolium. 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: 
