Witson :.NortH AMERICAN PERONOSPORALES 63 
reports have been taken into account in determining ‘the distribu- 
tion'of species; and mention is made of all reported hosts upon 
which no specimens have been seen. The determinations of all 
hosts’ have been'verified, with the resulting omission of a few of 
those previously published. These discrepancies are noted in the 
proper places by the insertion after the specimen of the previously 
published host name. ~All ‘specimens containing odspores are 
marked ‘by anh asterisk (*). Inasmuch as the hosts, or species 
closely related to the hosts, of all. the extralimital species of the 
genus occur in North America, these species: have been included 
in the key; and: brief mention made of them in their place in the 
Sequence of species. In conclusion I wish to express my appre- 
ciation of the courtesies: which have been shown me in this work 
by the loan of specimens, by critical suggestions and by the deter- 
mination of hosts. 
ALBUGO (Pers.) S. F. Gray, Nat. Arr, Brit. Pl. 
| £640. 1603 
Uredo § Albugo Pers. Syn. Meth. Fung. 223. 1801. 
Cystopus Lév. Ann. Sci. Nat. III. 8: 371. 1847. 
Conidiophores simple, cylindric or clavate, crowded into sub- 
epidermal sori without peridium or paraphyses ; conidia cylindric 
or globular, borne in chains, smooth, hyaline or with light-yellow 
contents ;_odspores globular, produced in various parts of the 
host, often separate from the conidia and forming more or less 
Conspicuous masses ; spores liberated by the rupture of the epi- 
dermis of the host ; germination always by zoospores. 
P Ty pe species, 4. Cruciferarum S. F. Gray = Uredo candida 
ers, ws 
Key to the species : 
Odspore tuberculate ; conidia globose or more or less cylindric, not as long as broad, if 
: discoid-the membrane of equal thickness throughout. 
OSspore with prominent tubercles; conidia similar, or the terminal smaller. 
© Odspore with.a few very large tubercles; conidial membrane of equal thickness 
r - 
Conidia globular, hyaline. — 
 Conidia and odspores large; hosts ; 
Papaverales, mainly Brassicaceae. 1. A. candida. 
* ° Conidia and odspores small; os 
oes Lean ae Boraginaceae. *:' te ; As sagen 
7s" *  \Conidia discoid, yellow. 3. A. tropica. 
