250 STUDY OF COJIMON PLAl>rTS. 



flower, for the most part, at widely different times, and 

 some of the genera exhibit among themselves such marked 

 structural differences as to obscure, except to a trained 

 eye, the common family characters. The contrast between 

 the simple, open flowers of the elder and the extremely 

 elongated corolla of species of Lonicera that have become 

 adapted to the visits of night-fljdng moths, is a striking 

 example. The student who wishes to familiarize himself 

 with this familj', which presents many interesting features, 

 will find in the course of spring and summer enough 

 indigenous species of the genera named above to enable 

 him to make a fairly extended comparative study. The 

 clue to the wide divergence of form, and the remarkable 

 series of colors exhibited by flowers of the different genera, 

 is apparently found in progressive adaptation to different 

 insect visitors.^ 



Another remarkable feature is the great difference of 

 habit exhibited by different members of the family, as 

 seen, for example, in a comparison of the slender, trailing 

 Linnaea with the coarse, upright Triosteum, or the climb- 

 ing species of Lonicera with the shrubs or trees of the 

 genera Sambucus and Viburnum. Even within the limits 

 of a single genus, as in the case of Lonicera and Viburnum, 

 wide differences of structure and habit present themselves, 

 affording an opportunity to observe adaptations that ap- 

 pear to have been acquired within comparatively recent 

 times. 



1 Cf . Miiller, Fertilization of Flowers, p. 299. 



