FLOWERS, THEIR STRUCTURE AND KINDS 



159 



of the stigma lobe and is not yet mature, so that the pollen 

 from the anthers of this flower cannot usually bring about 

 fertilization in this flower. Insects which visit this flower 

 carry the pollen to another flower where the stigma lobes are 

 mature, open and spreading. They are thus ready to receive 

 the pollen brought by the insect from the former flower. This 



Fig. 1 1 6. 



Flower of evening primrose with petals removed to show the four spreading lobes of the 

 stigma, and anthers beneath them. Petal at right, showing two stamens attached. 



mechanism of the flower necessitates cross-pollination for the 

 production of an abundance of seed (see chapter on pollination) . 

 252. The pollen grains are loosely held together by delicate 

 "cobwebby" threads, and the mass is slightly sticky, so that it 

 adheres readily to objects which it touches. These delicate 

 threads, shown in the photograph, fig. 118, are probably formed 

 by the partial gelatinization and shredding of the outer layer of 



