THE PLANT BODY 



41 



apogeotropic and erect. As the bud grows the scape elongates 

 and becomes temporarily diageotropic, as indicated in b and c. 

 When the flowers open, the scape and flower cluster become apo- 

 geotropic, and the erect flowers are thus exposed favorably for 

 cross-pollination by insects. Curiously enough, in the dandelion 

 the necessity for cross-pollination seems to have been lost in its 



Seed shedding 



Flowers 



FIG. 24. The response of the organs of the dandelion to light and gravity 



Note and be able to explain the positions assumed by the leaves and roots. The 



different positions of the flower stalk (scape) of the flowering head are indicated 



by the letters a-h. Consult the text for further discussion 



later history, since it has been found that its seeds may develop 

 without fertilization, though insect pollination, and its useful 

 effects, is not thereby precluded. When the seeds begin to form, the 

 scape moves downward (e and/), becoming again diageotropic in 

 its response to gravity, so that the seeds develop near the ground 

 (/), in a more protected position than the upright, apogeotropic 

 position of the open flowers (c?). When the seeds are ripe and 

 ready to be shed, the scape once more changes its responses to 

 the gravity stimulus from the diageotropic position (/) and 



