582 Species According to the Theory of Mutation. 
the breadth of the leaves and the length of the flower 
stalks. But these characters do not segregate in the 
offspring of the hybrids. They are presumably to be 
regarded as results of progressive specific differentiation. 1 
L. vespcrtina is, perhaps, a white-flowered variety of a 
red-flowered species which has disappeared. At any 
rate I do not think we shall go far wrong if we conclude 
that L. vespertina and L. diurna differ from one another 
partly by typical specific, and partly by varietal char- 
acters. 
GARTNER has repeatedly expressed exactly the same 
view and has illustrated it by the same instance. 2 He 
says that any doubt as to the specific difference between 
closely related species, as for instance between Lychnis 
diurna and L. vespertina, can be most easily removed by 
crossing; for if such species give exactly similar hybrids 
with some other, i. e., with a third species, the difference 
between the two is of a varietal nature only. But if this 
does not occur we have proof that the essential nature 
of the species crossed, although they appear closely related 
with regard to their external features, is specifically dis- 
tinct. For instance the two species of Lychnis just men- 
tioned give wholly different hybrids with Cucnbalus vis- 
cosns. On the other hand GARTNER lays stress on the 
fact that these species behave as varieties in regard to 
the color of their flowers when they are mutually crossed. 
Moreover Lychnis vespertina behaves as a variety with 
regard to the bending over of the teeth of the capsule, 
that is to say as a retrogressive variety of a species with 
the character of L. diurna. 
1 For a historical and critical treatment of the point, see a paper 
by R. ALLEN ROLFE, Hybridization Viewed from the Standpoint of 
Systematic Botany, Journ. Roy. Hort. Soc., April 1900, p. 197. 
'GARTNER. Joe. cit., pp. 581-582. 
