RYDBERG: STUDIES ON THE ROCKY MOUNTAIN FLORA 107 
S. elymoides Raf., I think that the latter name should supplant 
the other two. SS. lanceolatum J. G. Smith from Montana and 
S. marginatum Scribn. & Merrill from Wyoming are the two 
species of the range best differentiated and seem to connect the 
genus with Elymus. SS. insulare was described from north- 
eastern Utah, and S. ciliatum has been collected in Wyoming. 
ARACEAE 
This family is omitted altogether in the New Manual, although 
Acorus Calamus is recorded in my Flora of Colorado and Lysichiton 
camtschatcense (L.) Schott in my Flora of Montana. The former 
has also been collected in Montana by Butler. 
LEMNACEAE 
Lemna perpusilla Torr. is included by Nelson in his Manual 
with the remarks: “ Frequent; northern Wyoming to New York.” 
So far as I know this is wholly an eastern species. Specimens so 
labeled from the Rockies, which have come under my observation, 
are L. minor, L. minima, or L. cyclostasa, which all have been 
confused with it. 
COMMELINACEAE 
Professor Nelson admits two species of Tradescantia and gives 
the following key: 
Freely b hed; fil ts folded; y pub t in riblike li 1. T. laramiensis, 
Simple; filaments straight; ovary pubescent at the apex. 2. T. occidentalis. 
If these characters hold, as to separating the two species 
known to Professor N elson, the second one is not T. occidentalis, for 
the specimen designated by Dr. Britton as the type of Trades- 
cantia virginica occidentalis, viz., Rydberg 1380, from Thedford, 
Nebraska, has a branched stem and an ovary pubescent not only 
at the apex but almost to the base. It is not exactly like the 
type of T. laramiensis, however, for the lateral branches are 
shorter than the stem proper, the sepals are broader, the leaves 
broader, and the plant more glandular. In T. laramiensis the 
lateral branches about equal the stem, giving the plant a flat top. 
f these are specific characters, I do not know. If the two species 
of the New Manual are distinct, the second one should bear the 
Name T. universitatis Cockerell, for it was this form that Professor 
Cockerell described. 
