212 Rhodora [NOVEMBER 
near the close of its floral season, only a few plants remained in flower, 
though an occasional bud was seen. The greater part, however, 
were in seed, or, having lost their fruit, were drying up or dying, 
having accomplished their work as biennial plants. But the most 
surprising fact was that some of them were still in flower, a few even 
in bud, indicating a season not yet completed, in marked contrast 
with the familiar form (C. Hillit) at home. For in the neighborhood 
of Chicago, whether growing in the prairie or in the open parts of the 
dune region, C. Hillii is virtually out of flower by the 25th of July. 
Most of the plants at this date have already lost their seed, and by 
the first of August the stems are generally withered and dry. I have 
found it in flower as early as the 20th of June, and its season may be 
considered as lasting about six weeks, from the middle of June to the 
first of August, the plants being at their best during the first ten 
days of July. As contrasted with that of C. pumilum, July-Sept., 
its season is June-July. It comes into bloom a little later than C. 
Pitcheri (Torr.) T. & G., the earliest thistle to flower here. As the 
latter is almost confined to dunes close by the shore of Lake Michigan 
in our region, where the coolness of the water of the lake commonly 
retards the shore-plants a week or more beyond the time when the 
same species blossom farther away from the shore, this also is to be 
taken into account for the earliness of C. Pitcheri. I have collected 
it in flower as early as June 12th. It may also be found with flowers 
the first part of August, new branches or shoots having started from 
a stem or root that carries withered or dried stems at the same time. 
Its season is therefore longer than that of C. Hillii, the duration about 
the same as that of C. pumilum, but with an earlier beginning and 
closing. 
Another contrast between the two pasture-thistles, as I found them, 
is the more branching and somewhat taller habit of C. pumilum, and 
the resulting presence of a greater number of heads on the same 
individual. One commonly sees no more than three heads on a 
plant of C. Hillii. It often produces but a single large head crowning 
an unbranched stem 15 to 20 inches high. Occasionally five heads 
may be found on a more vigorous plant, or even more, particularly 
when the terminal bud of the main stem has been injured and branches 
are forced out from below. Nor is it so strongly armed as the eastern 
pasture-thistle, the prickles usually being weak. 
“But one of the chief distinctions lies in the roots of the two. This 
