INTERDEPENDENCE OF ORGANISMS 



II 



Pig. 5. Diagram of the flower of 

 a buttercup (Ranunculus), m, 

 petal; n, nectary on the base 

 of the lowermost petal; o, a se- 

 pal ■,p, a central group of separate 

 pistils; q, a mature, and r, an 

 immature anther. 



I. The adaptations of flowers to visitation by insects. 



Most flowers that profit by 

 insect visitation are composed of 

 the four whorls of organs seen in 

 the loosestrife flower. Two of 

 these sorts of organs, the stamens 

 and the pistils are essential to 

 seed production : the other two 

 sorts, petals and sepals (the floral 

 envelopes or perianth) are merely 

 accessory: they are often highly 

 serviceable, being adapted in 

 manifold ways to secure the visi- 

 tation of proper insects. These 

 may be wholly absent: and 

 stamens and pistils may be de- 

 veloped in difi^erent flowers, or even upon difl^erent plants, 

 as in the willows (fig. 4) . 



The type to which most insect-visited flowers conform 

 finds a simple expression in such a flower as that of the but- 

 tercup (fig. 5). There are many separate pistils and sta- 

 mens: petals and sepals are separate also, and alternate 

 in position: all the parts of these whorls are inserted on a 

 common receptacle at a common level: the nectar, secreted 

 under a little scale upon the base of each petal, is quite ex- 

 posed and readily accessible to almost all visitors ; and the 

 color is nearly uniformly yellow. 



These characters are variously modified in adaptation 

 to insect visitors: 



a) The flowers may become more showily colored and 

 more attractive to the eye. They may be specially 

 marked with darker or lighter streaks or blotches about 

 the entrance, as if to guide their visitors to the right 

 place. In the iris (fig. 6) there are three separate 



