354 VARIATIONS OF SPECIES. 
a proper dividing line between the two genera. We do not 
anticipate a loss of the genus Bidens, however, though prob- 
ably no collector would object to its thorough extermination 
from our flora, with all its “pitchforks” and "Spanish 
needles," together with the Desmodiums, which in autumn 
force the herborizer so extensively into their service in trans- 
porting their "fearfully and wonderfully made" legumes. 
As examples of the manner in which one genus may merge 
into another, and one species into another, we cite two in- 
stances which have lately fallen under our observation. The 
first is that of the G'ymnostichum Hystrix of Schreber. This 
remarkable grass was apparently separated from the Linnsean 
genus Elymus, upon the single character of the absence of 
glumes. In this section of the country, however, we find it 
with well developed glumes, which are persistent after the 
spikelets fall. The glumeless and intermediate forms also 
occur, but the one most common has rigid, awn-like glumes 
situated precisely as in Hlymus, of nearly an inch in length, 
and with one prominent nerve, being therefore triangular, 
though appearing terete. We have never found the pales 
dentate (as figured in Pl. 11 of Gray’s Manual) in any form 
of the species, and the “pedicels” are evidently the joints to 
which the glumes are attached, and are but little longer than 
in some species of Elymus. Were the spikelets appressed as 
in Elymus, it would strikingly resemble some species of the 
latter in aspect, and as there appears to remain no constant 
technical distinction of any importance, we see no reason why 
its former name, Elymus Hystrix L., should not be restored. 
Our second case is that of Eupatorium aromaticum L., 
which we are convinced is but a variety of K. ageratoides 
L. The latter species is very common at the North in low, 
rich woodlands, and has large, thin and smooth leaves, 
which, we think, vary very little in size and shape. On 
reaching Maryland (except in the mountains) and the coast 
this species seems to be supplanted by one having the same 
peculiar flower-heads, but lower and less branching, with 
