12 



GENERAL BIOLOGY 



U 



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entrances, each with its own guide streaks: and at the 

 center of the flower where there is no entrance there is a 



convergence of Hnes 

 "^^ ' """^ that often deceives 



: . ill-adapted visitors in 



I quest of the nectar. 



Not all the markings 

 upon flowers are thus 

 significant: doubtless 

 the deposition of pig- 

 ment follows struc- 

 tural lines and results 

 from physiological 

 causes, and may often 

 be wholly unrelated to 

 the exigencies of pol- 

 len transference. But 

 there is no mistaking 

 the meaning of the general fact that flowers adapted to 

 insect visitation are showy, while flowers whose pollen is 

 distributed by wind are generally inconspicuous; or, the 

 fact that humming- 

 bird flowers are scar- 

 let; or, that night 

 blooming flowers are 

 oftenmost white: or, 

 that the points of en- 

 trance for visitors are 

 conspicuously mark- 

 ed. 



b) The nectar ex- 

 hales a great variety 



of attractive scents, and the nectaries are sequestered in 

 various ways beyond the reach of ill-adapted visitors — 



Fig. 6. Top view of the flower of a wild iris 

 {Iris versicolor). 



Fig. 7. Diagrams of forms of corollas, a, bell- 

 form; b, funnel-form; c, tubular; d, spurred; 

 e, two-lipped; a, b, c are radial; d c^nd e, 

 bilateral. 



