296 



A TEXTBOOK OP BOTANY 



[Ch. VI, 5 



Not only a structural but also a physiological fitness to 

 the accompUshment of pollination occurs in flowers. Thus, 



most flowers are very strongly 

 phototropic, as one can see very 

 easily on any sunny bank or in 

 borders near buildings, and as can 

 be proven very strikingly by ex- 

 periment (Fig. 208). Thus they 

 are brought, and their faces set, in 

 the most conspicuous positions. 

 Again, many flowers, especially 

 those which present a special 

 alighting position to insects, are 

 very strongly geotropic (diageo- 

 tropic), and thus, no matter what 

 accident may befall the flower 

 stalk, the individual blossoms keep 

 their positions for the visiting in- 

 sect (Fig. 209). The tubes and 

 coronas of Narcissus and Daft'odils 

 are kept thus in their horizontal 

 positions, as can be proven bj' tying 

 a young flower stalk down hori- 

 zontally. Again, many flowers do 

 not open before rain, or else close 

 on its approach, and some few 

 flower-clusters turn upside down, 

 seemingly in adaptation against 

 damage to the pollen bj' water 

 (page 234). The stimuli concerned 

 are not in all cases clear, nor are 

 the weather predictions alwaj's 

 accurate, though in this they per- 

 haps succeed as often as our human forecasters with all their 

 exact instruments. Also, various movements of stamens 

 occur, partly effected mechanically, as in Mountain Laurel 



Fig. 20B. ~ A rlustcr of 

 Bellflowers, set in one-sided 

 light, showing phototropisni of 

 the fiowers. (Drawn from a 

 photograph.) 



