Origin of Different Kinds of Adaptations 361 
We meet with cases in which the same animal has at dif- 
ferent times of year different colors, as seen in the summer 
and winter plumage of the ptarmigan. There is no direct 
evidence to show how this seasonable change has been 
brought about; but from the facts in regard to Vanessa we 
can see that it might have been at least possible for the 
white winter plumage, for instance, to have appeared without 
respect to any advantage it conferred on the animal, but after 
it had appeared it may have been toa certain degree useful to 
its possessor. 
Amongst plants there are some very interesting cases of 
dimorphism and trimorphism in the structure of the flowers. 
Darwin has studied some of these cases with great care, and 
has made out some important points in regard to their powers 
of cross-fertilization.!1_ The common European cowslip, Prim- 
ula veris, var. officinalis, is found under two forms, Figure 5 
A and B, which are about equally abundant. In one the style 
is long so that the stigma borne on its end comes to the 
top of the tube of the corolla. The stamens in this form 
stand about halfway up the tube. This is called the long- 
styled form. The other kind, known as the short-styled form, 
has a style only half as long as the tube of the corolla, and 
the stamens are attached around the upper end of the tube 
near its opening. In other words, the position of the end of 
the style (the stigma) and that of the stamens is exactly 
reversed in the two forms. The corolla is also somewhat 
differently shaped in the two forms, and the expanded part 
of the tube above the stamens is larger in the long-styled 
‘than in the short-styled form. Another difference is found 
in the stigma, which is globular in the long-styled, and 
depressed on its top in the short-styled, form. The papillz 
1 Many of the facts as to the occurrence of these cases were known before 
Darwin worked on them; but very little had been ascertained in regard to the 
sexual relation between the dimorphic and trimorphic forms, and it was here that 
Darwin obtained his most interesting results, 
