136 



FERTILIZATION AND POLLINATION 



proterogynous. (Aner, andr, is a Greek root often used, in 

 combinations, for stamen, and gyne for pistil.) The dif- 

 ference in time of ripening may be an hour or two, or it 

 may be a day. The ripening of the stamens and pistils at 

 different times is known as dichogamy, and flowers of such 



character are said to be dichog- 

 amous. There is little chance 

 for dichogamous flowers to pol- 

 linate themselves. The holly- 

 hock is proterandrous. Fig. 222 

 shows a flower recently ex- 

 panded. The center is occupied 

 by the column of stamens. In 

 Fig. 223, showing an older 

 flower, the long styles are con- 

 spicuous. Many flowers are im- 

 perfectly dichogamous some 

 of the anthers mature simul- 

 taneously with the pistils, so 

 that there is chance for self-pol- 

 lination in case foreign pollen 

 does not arrive. Even when the 

 stigma receives pollen from its 

 own flower, cross -fertilization 

 may result. 



281. Some flowers have so 

 developed as to prohibit self- 

 pollination. Very irregular flow- 

 ers are usually of this cate- 

 gory. Regular flowers usually depend on dichogamy and 

 on the impotency of pollen on the pistil of the same flower. 

 Flowers that are very irregular and provided with strong 

 perfume are usually pollinated by insects. Gaudy colors 

 probably attract insects in many cases, but odor appears to 

 be a greater attraction. The insect visits the flower for the 



227. Toad-flax is an insect-pollinated 

 flower. 



