318 E. Jorgensen. 
Mendelian splitting up of hybrids descending from species with 
several pairs of different characters. In the course of time the 
variations of the climate very probably have brought about a 
differentiation which, perhaps especially indirectly on account of © 
enforced migrations in the neighbouring countries, has played an 
important part as to the present existing forms in a given region 
or country. Finally the seasonal dimorphism, discovered by 
Wettstein, is an important factor of differentiation, especially for 
producing primary forms with a different date of flourishing and 
a great number of different characters. 
To these reasons should, however, from my own experience, 
be added the influence of the locality, probably (chiefly) only its 
physical condition, especially in regard to the degree of dryness, 
and I have myself little doubt that this circumstance is a very 
important one. On the contrary, Wettstein seems to consider 
this influence as only of secondary importance in regard to the 
differentiation in species; he mentions it as only a cause of the 
evolution of different forms, which, however, by cultivation are 
said to fall back upon the common type of the species. The 
deciding cultures are unfortunately too vaguely described to serve 
as a proof for Wettstein’s statements. To a certain de- 
gree he may also be right; by culture of deviating forms under 
normal conditions we may expect descendants, more or less ap- 
proaching the typical form. Here, however, the different charac- 
ters most probably play a different part; some of them may be 
supposed to prove more fixed than others. On account of the 
importance of this question I will mention a very peculiar 
looking form of Euphrasia, which grows in Northern Norway 
in a few localities under unusual circumstances (compare E. mi- 
nima v. inundata). It is a very low, almost bare, pale form 
with exceedingly small flowers, having a much more regularly 
lobed and much less protruding corolla than usual. This plant 
was apparently wholly different from the common species of 
Euphrasia in the neighbourhood, E. latifolia, which here was a 
tall, hairy, deep-green plant with relatively large flowers and a 
well developed corolla. Nevertheless, after thorough examination 
of the forms in the different localities of the neighbourhood I 
feel quite convinced that we here have to deal with a variation, 
which most probably is hereditary, and can be accounted for by © 
the singular physical condition of the place of growth, a narrow 
