202 THE STRUCTURE OF FLOWERS. 



absolute in nature, so in this case, plants respond to the 

 influences brought to bear upon them, and each individual 

 may vary accordingly, but if the influence be permanent, then 

 the variation becomes hereditary, and one or other character is 

 fixed, and may be regarded as specific or generic as the case 

 may be. Should the environment change again, what may 

 have been constant for generations will be once more broken 

 up, and instability ensues. 



MuUer records several cases of such oscillations, as in 

 Pulsatilla vernalis, Dryas octopetala, Bibes petrmum, Gentiana 

 campestris, Veronica serpyllifolia, V. spicata. Walnut, Hazel, 

 etc. These vary from protandry through homogamy to 

 protogyny. He also mentions species which have not yet 

 arrived at complete protogyny, such as Sihhaldia procumbens 

 and Eanunculus alpestris, mountain species which are homo- 

 gamous ; while R. glacialis is sometimes even slightly pro- 

 tandrous. Papaver alpinum, Ardbis alpina, and Biscutella 

 laevigata are also described as homogamous. 



As the transitions from a conspicuous, protandrons, and 

 entomophilous or insect-fertilised flower to a homogamous 

 and autogamous or self-fertilised one, as well as to anemo- 

 phily, are the effects of degeneracy, they will be considered 

 more fully when that peculiar condition of floral structure 

 comes to be discussed.* 



• See Chaps. XXVI. and XXVII. 



