14 Contributions from the Gray Herbarium 
easily definable but confessedly artificial group, to which as a ge- 
neric unit the name Heliomeris of Nuttall (1848), based on H. multi- 
flora, should be applied. The aim of generic limitations, however, 
is not merely to provide an easy index to our real units the species, 
but to indicate their true genetic relationships so far as this can 
be done without too great a sacrifice of clearness and precision. 
After long and careful study of all these groups and repeated com- 
parisons of the related genera, I have come to believe that there are 
lines along which all the species of Heliomeris can be distributed 
into the genera to which they are most closely related — Vigwiera, 
Tithonia, and Hymenostephium — without thereby destroying the 
integrity of these groups, and with a distinct gain in the expression 
of the natural relationships of the species concerned. Evidence 
that such a treatment is in accord with the natural affinities of the 
plants concerned is shown by the fact that the species of Gymno- 
lomia, with the exceptions already noted, can be divided nearly in 
the order in which they stand in Robinson and Greenman’s revision - 
into groups which fall easily, and without requiring more than a 
very slight change in the statement of essential characters, into 
very natural subgenera, sections, and series already recognized 
among the species of Viguiera, Tithonia, and Hymenostephium. 
The significance of this fact will become apparent in the following 
discussion of the species in the order in which they appear in Rob- 
inson and Greenman’s revision. 
Gymnolomia Greggii Gray is in habit, foliage, and involucre 
almost the precise counterpart of Viguiera bicolor Blake of the 
series Brevifoliae of § Chloracra. The identity of involucre is espe- 
cially noteworthy, inasmuch as the Brevifoliae are somewhat aber- 
rant in their section in this regard. Aside from the lack of pappus 
and concomitant glabrity of the achene in the Gymnolomia, there 
is no distinctive character of more than specific consequence to be 
found between the species, unless it be the dilation of the corolla- 
base in the Gymnolomia, a feature of doubtful taxonomic impor- 
tance. G. cinerascens (Sch. Bip.) B. & H. I have never seen, and 
the combination of characters presented in its description is such 
as to leave its affinities in doubt. 
G. pinnatilobata (Sch. Bip.) B. & H., G. tripartita Rob. & Greenm., 
and G. tenuifolia (Gray) B. & H. fora a small group of low shrubby 
plants with more or less pinnately lobed or divided leaves, without 
