440 PROCEEDINGS OF THE AMERICAN ACADEMY. 
This may be its real affinity, but it is to be noted that Philippi repre- 
sents the style-branches as being recoiled through more than 360°. 
This would be highly exceptional in the Eupatorieae. Furthermore, 
the style-branches as shown in Philippi’s figures are unusually short 
for the tribe. Until material of this rare and local plant can be ob- 
tained and subjected to further study the species would better be left 
here, where Bentham placed it, but it would seem almost as likely to 
prove one of the Heliantheae, perhaps near Isocarpha. 
As explained elsewhere in this paper, the rudimentary annular 
or coroniform “pappus,” accredited in the past to several species 
hitherto placed in Ageratum, proves not to be a true pappus, i. e. & 
calycular structure exterior to the corolla, but only an annulus upon 
which the corolla itself is borne and which after the disarticulation and 
fall of the corolla sometimes is slightly accrescent. These species, 
destitute of a true pappus, must certainly be transferred to Alomia 
if that genus is to be kept distinct from Ageratum and they are so 
treated in the following revision. 
While in nearly all of the species concerned the presence or absence 
of a pappus is upon careful observation sufficiently evident and con- 
stant to permit a pretty ready separation of species into those which 
should be referred to Alomia on the one hand and those which would 
better be placed in Ageratum on the other, there are two exceptional 
species, Ageratum littorale Gray and A. maritimum HBK., in which 
the distinction breaks down absolutely. Here the pappus may be 
entirely wanting, it may consist of minute teeth, very short and slightly 
exterior to the corolla, or finally it may develop into a perfectly definite 
and conspicuous scale-pappus. These marked variations in pappus 
occur in individuals of precisely similar habit, and so far as ean be | 
ascertained are accompanied by no concomitant changes of structure. 
This wide intra-specific variation presents, of course, a technical 
difficulty in delimiting the genera Ageratum and Alomia. Howevel, 
it is to be remembered that calvous forms in normally pappus-bearing 
Compositae are by no means rare and must be accepted as one of the 
inherent difficulties of the group. It would be highly artificial to 
transfer to Alomia the calvous forms of Ageratum littorale and fee 
maritimum, nor does it seem best to unite with the otherwise consis- 
tently pappus-bearing genus Ageratum the consistently calvous genus 
Alomia because in certain exceptional species an abortion of the pappus 
occurs inconstantly, as it does also in T'richogonia menthaefolia Gardn., 
Calea peduncularis HBK., and various other Compositae in whic’ 
the loss of pappus can in no sense be regarded as having genere 
significance. 
