May 19, 1913 55 
and flat, the second series prolonged into a stout spine, thick- 
ened upward and equaling the inner in length, the inner ones 
weaker and unarined: flowers whitish: pappus brown and plu- 
inose. 
Collected along Thompson river in the canyon just east of 
Estes Park, Larimer county, Colorado, August 23, 1912, no, 
4803. I suppose the relationship of this Carduus is with C. 
americanus (Gray) Greene, and C. spathulatus Osterhout, but 
the small heads and long thickened bracts, not at all fimbriate, 
separate it from these. The long bracts might suggest C. gre- 
seus Rydb., but C. modestus is a much more slender plant with 
smaller heads, and the long bracts are not flat as they are in C. 
gVIseus. 
In his account of some hybrid thistles in Bull. Torr. Club 
37: 584, Dr. Rydberg made a plant which I collected here a 
hybrid of C. gréseus and C. laterifolius, bnt I should say that 
the hybrid is rather of C. modestus and probably C. americanus, 
since it has the long stout bracts of C. modestus, but with some 
of them showing fimbriation. 
Along Thomson river as it leaves Estes Park, and in the 
canyon near there, are a number of species of Carduus which 
are of interest to the student of these things because of the in- 
termediate forms. Here occur C. americanus (Gray) Greene, C. 
laterifoltus Osterhout, and the one here described, C. modestus. 
All of these appear to have hybridized, and possibly there are 
crosses of hybrid with hybrid; at any rate the forms are per- 
plexing and difficult of classification. 
‘ 
Carduus acuatus sp. nov. 
Seemingly a short-lived perennial 8dm. or more high, con- 
siderably arachnoid pubescent, rather stout, leafy to the ends of 
the branches: leaves linear in outline, acuminate, divided about 
half way to the midrib, the lobes again divided into two or three 
acuminate parts prolonged into stout, sharp spines; lower leaves 
1 to 2dm. long, becoming smaller upward, all armed with the 
uncommonly stout needle-like spines, the under surface matted 
woolly pubescent, the upper side green but considerably arach- 
