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 to a 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 papillae 



i.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. 



