THE FLOWER 127 



250. In both these cases, and countless others, tlie inflo- 

 rescence — mode of arrangement of the flowers — is deter- 

 mined by the need of cross-fertilization. 



EFFECT OF CROSSING 



251. The arrangements for cross-fertilization are ex- 

 tremely varied and in many cases extraordinarily compli- 

 cated. It could not well be doubted that such elaboration 

 has been evolved because some important benefit is derived 

 from intercrossing. And experiment goes to show that 

 this is actually the case. When seeds derived from both 

 self-fertilization and cross-fertilization of the same plant are 

 grown side by side, the offspring of cross-fertilization gen- 

 erally outstrips that produced by self-fertilization. In 

 spite of the fact that a small number of species are propa- 

 gated indefinitely without intercrossing (seedless plants, 

 reproduced vegetatively), and as far as is known without 

 harmful results, the important truth remains that inter- 

 crossing is a means of giving increased vigor to seedlings. 



Supplementary Reading 



1. Adaptations for Securing Intercrossing. Gray's " Structural 

 Botany," p. 220 and following. 



2. The Pollination of Orchids. C. M. Weed's " Ten New England 

 Blossoms," Nos. VI. and YII. 



3. " The Mayflower." Same source, No. II. 



4. The Industriousness of Bees, and the Perception of Color by 

 Insects. Sir John Lubbock's " Flowers, Fruits, and Leaves," pp. 11-14. 



Supplementary Studies : Fieldwork on the Ecology 



of the Flower 



252. The account of adaptations to secure cross-fertilization given in 

 this chapter is necessarily brief, hardly more than suggesting some general 

 principles. Subjects not touched, but well wortii study in the field, are : 

 Attraction of Insects (a) by colors, (6) by grouping flowers, (c) by scent ; 

 Opening of Flowers at special times to receive special classes of insects ; 

 Guides to Honey, («) spots and streaks, (6) conformation of floral parts ; 

 Reward to Insects, (a) honey and sap (with distribution and form of 

 secreting organs) , (&) pollen, (c) edible tissue, (cZ) shelter; Dusting the 

 Insect, (a) by irritable stamens (Barberry), (6) by springing stamens 



