THE CYCLE OF LIFE : FLOWERS 



51 



cone-bearing trees, and 

 the catkin-bearing trees. 

 41. Homology and anal- 

 ogy in the flower. If you 

 have studied several dif- 

 ferent kinds of flowers, 

 you must have noticed 

 the very great differences 

 among petals of different 

 species or among pistils. 

 Indeed, you will often 

 have some difficulty in 

 making up your mind 

 whether some particular 

 structure is one of the 

 regular parts of a flower 

 or something totally dif- 

 ferent. A part of the fas- 

 cination that many peo- 

 ple find in studying new 

 varieties of wild flowers 

 is that of recognizing 

 famihar structures under 

 strange disguises, or like 

 that of solving puzzles. 

 Stamens may be large or 

 small, with long filaments 

 or with none, standing 

 freely or fused with one 

 another or with the co- 

 rolla. Similar modifica- 

 tions are found in the 

 other parts. Some stu- 

 dents of plant life go 



even farther and point out that stamens and carpels, as well 

 as petals and sepals, are special kinds of leaves (see Fig. 25, 



Fig. 24. Hand pollenation in the vanilla 



flower 



Instead of importing the needed insect to carry 

 on pollenation, the raisers of vanilla decided to 

 hire women and children to go from flower to 

 flower and pollenate by hand. In the orchids 

 the stamens are fused with the stigma, placing 

 the anthers above the stigma in such a way as 

 to make self-pollenation absolutely impossible. 

 an, anther; p, pollen masses; s, stigma. A, gen- 

 eral view of flower; B, position of hands and 

 needle in artificial pollenation; C, needle lifting 

 pollen masses; D, anther raised to expose pollen 

 masses; E, style raised to show opening in 

 stigma; F, longitudinal section to show relative 

 positions of anther and stigma: G, longitudinal 

 section after pollenation, showing pollen masses 

 in the stigma. All the vanilla beans in the Sey- 

 chelles Islands are grown with hand pollenation 



