228 Plant Life and Evolution 



mum in certain highly specialized monocotyledons 

 like the orchids and canna, where usually only a 

 single functional stamen is present. Where the 

 number of stamens is reduced, this is almost always 

 associated with change from the original radial 

 symmetry of the flower to a marked bilateral sym- 

 metry. This is seen in the cases cited and also in 

 such dicotyledons as the mints and bignonias, in 

 which the floral leaves are united into a tubular or 

 trumpet-shaped corolla. 



Color and Scent in Flowers. With these modifi- 

 cations in structure there are associated a great va- 

 riety of vivid colors, so that these specialized flow- 

 ers include most of the more showy species under 

 cultivation. Another common phenomenon is the 

 development of the characteristic scents in flowers, 

 these being, in the opinion of many modern students 

 of cross-pollination, the most potent means of at- 

 tracting insect visitors. Color and scent may both 

 be associated with the secretion of nectar, the prin- 

 cipal object of the visits of butterflies and many 

 other insects. 



How far insects are able to discriminate the 

 colors of flowers, and especially the elaborate 

 color-patterns of the so-called " honey guides," 

 etc., is much in need of thorough investigation. 

 While the earlier investigators attributed to insects 

 a capacity for color discrimination not entirely 

 warranted by the facts, there is no question 

 that the conclusions of some of the recent oppo- 



