426 



POLLINATION OF FLOWERS 



402. Protection of pollen from unwelcome visitors. It is 



usually desirable for the flower to prevent the entrance of 

 small creeping insects, such as ants, which carry little pollen 

 and eat a relatively large amount of it. The means adopted to 

 secure this result are many and curious. In some plants, as 

 the common catchfly, there is a sticky ring about the peduncle, 

 some distance below the flowers, and this forms an effectual 

 barrier against ants and like insects. In a few plants, as the 



FIG. 325. Bees visiting flowers 



At the left, a bumblebee on the flower of the dead nettle; below, a similar bee in 

 the flower of the horse-chestnut ; above, a honeybee in the flower of a violet. 

 Modified. After Behrens 



teasel and the cup plant (Silphium perfoliatum), rain water col- 

 lects at the junctions of the leaves with the stem and forms 

 an effectual barrier against creeping insects. Very frequently 

 the calyx tube is covered with hairs, which are sometimes 

 sticky. How these thickets of hairs may appear to a small 

 insect can perhaps be realized from Fig. 32 6. 1 



1 On protection of pollen, see Kerner and Oliver, Natural History of 

 Plants, Vol. II, pp. 95-109. 



