312 



FLOWERS 



As to the sense of smell, however, insects are very keen. 

 Fragrant flowers which are inconspicuous are visited much 



more than are showy ones 



whichhavenoodor. Night- 

 flying moths locate flowers 

 readily by their fragrance, 

 and there are some flowers 

 which open and give out 

 their fragrance only at 

 night ; the moonflower and 

 night-blooming cereus are 

 famous for this. There is 

 reason to believe that many 

 insects detect odors which 

 we are quite unable to per- 

 ceive. The skunk cabbage 

 and the carrion-flower have 

 decidedly disagreeable 

 odors. These odors, hke those of decaying flesh, are at- 

 tractive to flies. 



c. Examples. — In their relation to insects there is a 

 general difference between flowers with actinomorphic 

 (regular) corollas and those with zygomorphic (irregular) 

 ones (see page 287). The former generally have a con- 

 siderable variety of insect visitors, while the visitors of 

 the latter are more limited as to kinds. It is among 

 zygomorphic flowers that we find those highly speciahzed 

 forms which make pollination possible by certain insects 

 only. 



Flowers with regular corollas and spreading perianths, 

 like buttercups or wild roses or apple blossoms, are open 

 to all comers. Their pollen and their nectar may be 



Fig. 132. — A flower of Petunia visited 

 by a hawk moth. Note the long 

 corolla tube of the flower, and the long 

 mouth part of the insect. 



