254 SHADE PLANTS OF THE ALPINE FORESTS 



much darker in colour above. The veins are very 

 prominent. 



Despite the specific name, "bifiora," each shoot 

 usually bears only a single flower, and not two, in 

 the Alps. The flowers are the smallest of any Swiss 

 Violet. They are bright yellow in colour, streaked 

 with brown. The plant attracts flies, which abound 

 in the forests, and is cross-pollinated by their agency. 

 The mechanism for ensuring cross-fertilisation is 

 much the same as in the case of the Field Pansy, 

 described on p. 161. 



The flowers of this Violet probably correspond 

 more closely to the ancestral form, than those of any 

 other Swiss member of the genus. In the Field 

 Pansy (Viola tricolor, Linn.), the colour has become 

 wholly or partly changed from yellow to blue, and 

 the size of the flower has been greatly increased in 

 order to make them acceptable to humble-bees and 

 butterflies. In the case of the Long-spurred Violet 

 (Viola calcarata, Linn.) (p. 128), the flowers have 

 specialised for butterflies exclusively. To this end, 

 the colour has become "fixed" to a pale blue, the 

 size of the flower still further enlarged, and the spur 

 enormously lengthened. 



THE MAY LILY. 



One particular section (Convallariese) of the Lily 

 family, Liliacese, consists almost entirely of shade- 

 plants, which differ in several important respects from 

 other members of the order. The underground stems 



