130 



FERTILIZATION AND POLLINATION 



204. 



azalea, 

 opening 

 by termi- 

 nal pores. 



265. Most floivers are so constructed as to increase the 

 chances of cross-pollination. We have seen (261) that 

 the stigma may have the power of selecting foreign pol- 

 len. The commonest means of insuring cross- 

 pollination is the different times of maturing cf 

 stamens and pistils in the same floiver. 

 In most cases the stamens mature first : 

 the flower is then proterandrous. When 

 the pistils mature first the flower is 

 proterogynous. (Aner, andr, is a Greek 

 root often used, in combinations, for 

 stamen, and gijne 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 dichogamous. There is little chance for dicho- 

 gamous flowers to pollinate themselves. Many flowers are 

 imperfectly dichogamous some of the anthers mature simul- 

 taneously with the 

 pistils, so that there 

 is chance for self- 

 pollination in case 

 foreign pollen does 

 not arrive. Even 

 when the stigma re- 

 ceives pollen from 

 its own flower, 

 cross -fertilization 

 may result (261). 

 The hollyhock is 



206. Flower of hollyhock; proterandrous. proterandrOUS 



Fig. 206 shows a flower recently expanded. The center is 

 occupied by the column of stamens. In Fig. 207, showing 

 an older flower, the long styles are conspicuous. 



