264 ROBINSON. 
II. A DESCRIPTIVE REVISION OF THE COLOMBIAN 
EUPATORIUMS. 
In assembling data for a revision of the Eupatoriums of Mexico 
and Central America the writer was some months ago led to scrutinize 
the existing evidence as to their possible range-extensions into the 
northern portions of South America. The questions which arose were 
briefly, in how far is the Isthmus of Panama a path of plant-migration, 
or conversely, to what extent has this narrow neck of relatively low 
land, in recent geologic times, or the pre-existing marine channel, at a 
more remote epoch, acted as an effective barrier to plant-distribution? 
Correlated with this somewhat abstract inquiry, arises a more 
concrete oné when it is borne in mind that most of the larger South 
American collections have been studied in Europe, while nearly all 
recent work upon the Mexican and Central American floras has been 
done in the United States. Thus it becomes pertinent to inquire 
whether to any serious extent there has been unconscious duplication 
in the results — whether, for instance, of the many species and varie- 
ties described as new from Mexico and Central America, some portion 
may not precisely duplicate plants present in and perhaps already 
described from South American collections, which are sparingly if at 
all represented even in the larger herbaria on this side of the Atlantic. 
At all events, to put classification of the very numerous Eupatoriums 
north of the Isthmus on a more secure footing, it seemed desirable, if 
not actually necessary, to give systematic attention at the same time 
to those of the adjacent portions of South America. For this purpose 
a provisional revision of the Colombian Eupatoriums was begun 1D 
October, 1917. To the usual difficulties incident to tropical work a 
deplorably inadequate material, scattered types, fragmentary litera- 
ture, uncontrasted descriptions, faulty and inconsistent records — 
there has in the present instance been added the impossibility of com- 
municating with several important European herbaria. However, 
by piecing together all available bits of fragmentary data, a treatment 
is here presented, which includes more than three times as many . 
Colombian Eupatoriums as have been heretofore recorded in any 
single paper. pe, 
It has long been customary in most minor works dealing with tropical 
