THE WORK OF FLOWERS 297 



a few green leaves placed in it will be of great 

 assistance in this respect.) 



The opening of the flower seems to be caused by 

 more rapid growth of the inner side of the petal; 

 the closing by more rapid growth of the outer side of 

 the petal: how far the latter process would go if the 

 other petals did not hinder it, may be easily seen by 

 cutting them away. 



It appears, then, that the petals protect the pollen 

 from rain and dew ; we have already found that the 

 calyx prevents the inner parts of the flower from 

 drying up during their development, and it seems 

 probable that the petals serve the same function also. 

 It would be easy to determine this point by a few 

 experiments. But, so far as protective purposes go, the 

 most striking thing about the petals, i. e., their color, 

 would seem to be useless. We may therefore ask, Of 

 what use is the color of the flower? It is quite safe to 

 say that every one has been told that insects are 

 attracted to flowers by their colors. The petals, with 

 their bright and showy colors, have been compared 

 to sign-boards, which advertise to the bees the pres- 

 ence of the honey and pollen of which they are in 

 search. The insects, in their visits, carry pollen from 

 flower to flower, and so enable the flower to set fruit. 



It is true that there exist a great number of devices 

 for making the flower conspicuous, chief of which are 

 striking color and the grouping of flowers in masses. 



