ADAPTATIONS FOR INTERCROSSING. 217 



400. The actual proposition, simply stated, is that flowers are 

 habitually intercrossed, and that there are manifold structural 

 adaptations which secure or favor intercrossing, to such extent 

 as to justify the proposition. The proof of the proposition is an 

 induction from a very great number of particular observations. 

 That intercrossing is beneficial is a rational inference from the 

 array of special adaptations for which no other sufficient reason 

 appears, or (to resume the metaphor) from the vast pains which 

 seem to have been taken to secure this end. This inference has 

 been to some extent confirmed by direct experiment. 1 



401. Separation of the sexes is a direct adaptation to inter- 

 crossing, rendering it necessary between individuals in dioecious, 

 and largely favoring it in most monoecious and polygamous 

 flowers. Strictly close fertilization can occur in hermaphrodite 

 flowers only ; but it is in these that the most curious adaptations 

 for intercrossing are revealed. 



402. The agencies to the one or the other of which most 

 flowers are structurally adapted in reference to intercrossing are 

 mainly two ; viz., the winds and animals, of these chiefly insects. 

 Delpino has accordingly classified flowers into Anemophilous and 

 Entomophilous ; literally wind-lovers and insect-lovers, but de- 

 noting wind-fertilized and insect-fertilized, according to the 

 agent by which pollen is transported. 2 There are hermaphrodite 

 and unisexual flowers of both classes, but most wind-fertilized 

 flowers are unisexual. 



403. Wind-fertilizable or anemophilous flowers are mostly neu- 

 tral or dull in color, destitute of odor, and not nectariferous. 

 Their principal structural adaptations to this end, besides the 

 separation of the sexes in most of them, are the superabundance, 

 incoherency, dryness, and lightness of the pollen, rendering it 

 very transportable by wind and currents of air. The immense 

 abundance of pollen, its lightness, and its free and far diffusion 

 through the air in Pines, Firs, Taxodium, and other Coniferae, 

 are familiar. Their pollen fills the air of a forest during anthe- 

 sis ; and the "showers of sulphur," popularly so-called, the 

 yellow powder which after a transient shower accumulates as 

 a scum on the surface of water several or many miles from the 



1 Darwin, The Effects of Cross and Self-Fertilization in the Vegetable 

 Kingdom, London, 1876. American Edition, New York, 1877. 



2 Ornithophilous, i. e. bird-fertilized, flowers are to be ranked with entomo- 

 philous. The large blossoms of Trumpet Creeper (Tecoma radicans) and 

 of Trumpet Honeysuckle (Lonicera sempervirens), and others, are commonly 

 visited and probably fertilized by humming-birds as well as by moths ; and 

 other birds are known to play a similar part in equatorial regions. 



