318 PLANT-LIFE 



allowing the remaining five to erect themselves and 

 behave in the same way. Having shed their pollen, the 

 stamens wither. Insects which visit the flower at this 

 stage in quest of honey become dusted with pollen, and 

 carry it to another flower with a ripe stigma ; the stigmas 

 of the flower under notice are not ripe, and remain 

 closed. Later they ripen and radiate, fully exposing 

 their sensitive surface, and an insect visitor coming from 

 a neighbouring flower, and laden with pollen, uncon- 

 sciously deposits some of the grains on the stigmatic 

 surface. Thus cross-pollination is secured. 



The familiar Primrose is a remarkable example of 

 provision for cross-fertilization. Some Primrose plants 

 bear flowers with long styles, while others produce short- 

 styled flowers. The lower portion of the corolla in both 

 cases is tubular. In the long-styled, or " pin-eyed," 

 flowers the stigma appears at the top of the tube, and 

 the anthers of the stamens are placed about half-way 

 down. In the short-styled, or " thrum-eyed," flowers 

 the anthers are at the top of the tube, and the stigma 

 reaches only about half-way up. Honey in both kinds 

 of flowers is secreted at the base of the ovary at the 

 bottom of the corolla tube; it can be reached only by 

 long-tongued insects. If we take a bristle, and insert it 

 into the tube of a " thrum-eyed " flower, pollen will 

 adhere to it just at the level of the anthers. Now, in- 

 serting the bristle into a " pin-eyed " flower, we find 

 that the attached pollen will coincide with the level of 

 the stigma. Further, when we withdraw the bristle 

 from this flower, it will be marked with pollen from the 

 anthers half-way down in the tube, and this mark will 

 be on an exact level with the stigma of a " thrum-eyed " 



