INTERDEPENDENCE OF ORGANISMS 29 



3. Offers what alighting place. 



4. Is entered how far. 



5. Stigma or anther touched first. 



6. Pollen carried how. 



7 . ■ Number of flowers visited in succession without inter- 

 vening long flight. 



8. Number of flowers visited per minute. 



9. Well or ill-adapted for pollination by this insect. 



5. Precise adaptation between flowers and insects, leading to 



mutual dependence. 



It will have been noticed ere this that the flowers which 

 are very irregular or have closed corollas, or secrete their 

 nectar at the bottom of deep and narrow tubes or spurs, 

 have fewer visitors than those that are open and regular. 

 Only those insects which have long proboscides, or which 

 are endowed w4th special ability at forcing passageways 

 can obtain their stores. Flowers thus specialized receive 

 the usual good and ills of specialization; they enjoy 

 especially efficient aid when their proper visitors are abun- 

 dant and lack it when these are scarce. It is in the relations 

 existing between these most highly specialized flowers and 

 their few guests that one sees the most remarkable phe- 

 nomena of fitness and learns the extent and the precision 

 of mutual adaptation. 



Such adaptations are peculiar and special, and no general 

 outline can be given for their study: instead, an example 

 will be detailed and a few suggestions offered, and not a 

 formal outline. 



For example, let us consider the pollination of the marsh 

 weed commonly known as turtleheads {Chelone glabra). 

 Its rather large white flowers are arranged in four vertical 

 rows at the top of the leafy stem. They are strongly 

 bilateral and have abundant pollen and nectar, so guarded 



