80 GATES : THE VALIDITY OF HELIANTHUS ILLINOENSIS 
In the American Naturalist (42: 73-80. F 1908), David 
Starr Jordan formulates what he terms the “ Law of Geminate 
Species” in these words: “ Given any species, in any region, the 
nearest related species is not to be found in the same region nor 
in a remote region, but in a neighboring district separated from 
the first by a barrier of some sort or at least by a belt of country, 
the breadth of which gives the effect of a barrier.’ This state- 
ment is given in slightly different words and amplified to make its 
application to plants more obvious by A. E. Ortmann (Science 
II. 27: 427. 1908) as follows. ‘Closely allied species occupy 
neighboring areas; more or less closely allied species, occupying 
the same or nearly the same territory, generally possess different 
habits.’ This makes it clear that ecological as well as geographic 
segregation enters into the composition of species. Stated upon 
an ecological basis, this principle is that closely allied species ought 
not to occur within the same association in a given geographic 
area. Variations in any given species are always more or less 
marked according to local or edaphic factors. This variation, occa- 
sioned by environment, leads to extreme types between which 
there may be every gradation. In some cases only the extremes 
are noticeable but wider observation will reveal the intermediate 
steps. Ecological consideration of the factors involved clearly 
shows that these types are variations of one species. When vari- 
ation in ecological factors has led to the production of two or more 
apparently well-characterized types, it is frequently necessary, for 
the sake of definiteness and conciseness in referring to them, to 
give them recognized names. These names, however, are not of 
really specific rank. In general, the normal type or the one from 
which the variations occur ought to bear the specific name and the 
well-characterized variations, especially those which are connected 
with the normal form by comparatively few gradations, ought to 
bear subspecific names, reserving the term “ variety” to horticul- 
ture where it more properly belongs. Ortmann (Science II. 27: 
429. 1908) sums up the idea in the form of a rule. “If further 
studies should show that there is segregation, geographical or 
ecological, between these forms, then they are species ; if not, they 
are varieties (= subspecies), which fact then also will be expressed 
in their morphological condition, one form running into the other 
at least in certain parts of their ranges.’’ 
