Die Euphrasia-Arten Norwegens. 317 
Summary. 
The Norwegian species of Euphrasia — as in general is 
the case with all species of the section Semicalcaratæ Benth. — 
only differ from each other in degree, not in definitely different 
charakters. It is therefore difficult or impossible to distinguish 
them quite certainly, the more so as all species generally are very 
variable und comprise numerous forms. The term species here 
is used in the same sense as in the well-known monograph of 
Wettstein. ; 
This variability of the species seems at present to be caused 
by the existence of a great many forms, each of which appa- 
rently is tolerably constant, but by crossing with the others and 
subsequently splitting up, according to the Mendelian laws, has 
given rise to an apparently infinite series of forms, as yet mor- 
phologically not distinguishable. These primary species — if 
they exist, which has not been proved by cultures — are of 
course of a much lower systematic value than Wettstein’s 
species, the latter comprising a, more or less, great number of 
the former. 
As to the causes which have produced the primary forms 
or species we have as yet no certain knowledge; it is, however, 
very probable that the same causes to which Wettstein de- 
scribes the differentiation of the genus in the species which he 
accepts, also have been the most important for the evolution of 
the primary forms. These causes are differences in climate, 
differences of the seasons, and hybridization. I have already 
mentioned the latter cause, which — according to my personal 
experience — I should consider the most important to account 
for the present state of things, producing from the existing mul- 
titude of forms — whether they are considered primary species 
or not — a fast inextricable jumble answering to the well-known 
