ROBINSON:— ALOMIA, AGERATUM, AND OXYLOBUS. 439 
from Ageratum and Trichogonia solely on the absence of pappus, the 
genus may well have a composite — at least a double — origin. 
Either a Trichogonia, on the loss of its plumose pappus-bristles (a 
condition known to occur in 7’. menthaefolia and T. salviaefolia Gardn.), 
or an Ageratum, on the complete abortion of its often obsolescent scale- 
pappus, would become as to technical characters an Alomia, and the 
fact that the genus Alomia, as now circumscribed, contains species of a 
wide range of habit, extending on the one hand from the original A. 
ageratoides, with distinctly ageratoid habit, to A. dubia, on the other, 
which except for the lack of pappus would certainly be placed in 
Trichogonia, it appears by no means unlikely that the elements now 
grouped in Alomia may have come in part from an ageratoid and in 
part from a Trichogonia-like ancestry. 
Although from these considerations Alomia may seem an artificial 
group, its components certainly have close affinity and our present 
knowledge does not permit any improvement of the situation either 
by dividing the genus on trifling traits of habit or by merging it bodily 
with any of the neighboring genera. 
The three species here grouped as a new subgenus, Geissanthodium, 
possessing softer much imbricated involucral scales (striate in the 
manner of Brickellia), form an interesting strain, a small presumably 
natural group. After careful comparison ‘of A. alata Hemsl. and 
Ageratum callosum Wats. it is impossible to see any grounds for their 
generic separation. Either Ageratum callosum must be referred to 
Alomia or the genus Alomia must be transferred to Ageratum. The 
close relationship of the third species of this subgenus, the South 
American A. Regnellii Malme, although less convincing, seems highly 
probable to judge from Malme’s description and figures. Some spe- 
c1ous arguments might be advanced for the separation of these three 
Species as a new genus, but their distinctions from other species of 
Alomia are not strong. Involucral characters in nearly related genera 
are seen to be highly inconsistent and it is to be noticed that the im- 
brication of the scales is by no means so striking in the Brazilian A. 
gnellii as in the Mexican species. Nor is the undifferentiated 
corolla-tube a strong character. It seems best therefore to treat the 
group merely as a subgenus. 
Alomia tenuifolia (the genus Lycapsus of Philippi), a xerophytic 
shrub confined to a small island off the coast of Chili, is still ob- 
Scure. It does not appear to be represented in the leading European 
or North American herbaria. Bentham, judging it merely by the 
description and crabbed little figures of Philippi, placed it in Alomia. 
