ANIMALS AND PLANTS 247 



visits are prevented. In more highly specialized flow- 

 ers the parts are usually so modified as to restrict the 

 insect visitors to a smaller number ; in extreme cases 

 often a single species, or a few species belonging to a 

 single genus. Thus in the buttercup family we find not 

 only the generalized type of flower of Ranunculus, or 

 Anemone, but the highly specialized ones of the colum- 

 bine (Aquilegia) (Fig. 50), larkspur (Delphinium), and 

 monk's-hood (Aconitum). In these the parts of the 

 flower are very much changed, and in the columbine 

 and larkspur deep nectaries are developed which are 

 accessible only to insects with long tongues, like 

 bumblebees or butterflies; or in the case of the scar- 

 let-flowered columbines, they are visited by humming- 

 birds. It is interesting to note that in these extremely 

 specialized Ranunculacese there has been little depart- 

 ure in the number of parts from the primitive buttercup, 

 and all the parts remain quite separate. 



It sometimes happens that the flowers themselves 

 remain inconspicuous, but are grouped together with 

 showy colored bracts about the inflorescence, and these 

 showy leaves serve to attract insects just as the petals of 

 other flowers do. Familiar examples of this are seen in 

 the common "calla-lily," (Fig. 55), where the large white 

 spathe surrounding the small flowers is very conspicu- 

 ous, and many other aroids, such as species of Anthu- 

 rium, possess these showy spathes. Another similar 

 case is that of certain species of Cornus, like the beau- 

 tiful dogwood (Q.florida, Fig. 55, B), where the group 

 of small flowers is surrounded by four large white 

 bracts, the whole looking like a large four-parted flower, 

 and the tree when in bloom is exceedingly showy, 



