SECTION 13.J FERTILIZATION. 115 



Close Fertilization occurs when the pollen reaches and acts upon a stigma 

 of the very same flower (this is also called self-fertilization), or, less closely, 

 upon other blossoms of the same cluster or the same individual plant. 



Cross Fertilization occurs when ovules are fertilized by pollen of other 

 individuals of the same species. 



Hybridization occurs when ovules are fertilized by pollen of some other 

 (necessarily some nearly related) species. 



332. Close Fertilization would seem to be the natural result in ordi- 

 nary hermaphrodite flowers ; but it is by no means so in all of them. More 

 commonly the arrangements are such that it takes place only after some 

 opportunity for cross fertilization has been afforded. But close fertiliza- 

 tion is inevitable in what are called 



Cleistogamous Flowers, that is, in those which are fertilized in the flower- 

 bud, while still unopened. Most flowers of this kind, indeed, never open 

 at all ; but the closed floral coverings are forced off by the growth of the 

 precociously fertilized pistil. Common examples of this are found in the 

 earlier blossoms of Specularia perfoliata, in the later ones of most Violets, es- 

 pecially the stemless species, in our wild Jewel weeds or Impatiens, in the 

 subterranean shoots of Amphicarpsea. Every plant which produces these 

 cleistogamous or bud-fertilized flowers bears also more conspicuous and 

 open flowers, usually of bright colors. The latter very commonly fail to 

 set seed, but the former are prolific. 



333. Cross Fertilization is naturally provided for in dioecious plants 

 (249), is much favored in monoecious plants (249), and hardly less so in 

 dichogamous and in heterogonous flowers (338). Cross fertilization depends 

 upon the transportation of pollen ; and the two principal agents of convey- 

 ance are winds and insects. Most flowers are in their whole structure 

 adapted either to the one or to the other. 



334. Wind-fertilizable or Anemophilous flowers are more commonly 

 dioecious or monoecious, as in Pines and all coniferous trees, Oaks, and 

 Birches, and Sedges ; yet sometimes hermaphrodite, as in Plantains and 

 most Grasses ; they produce a superabundance of very light pollen, adapted 

 to be wind-borne; and they offer neither nectar to feed winged insects, 

 nor fragrance nor bright colors to attract them. 



335. Insect-fertilizable or Entomophilous flowers are those which 

 are sought by insects, for pollen or for nectar, or for both. Through their 

 visits pollen is conveyed from one flower and from one plant to another. 

 Insects are attracted to such blossoms by their bright colors, or their fra- 

 grance, or by the nectar (the material of honey) there provided for them. 

 While supplying their own needs, they carry pollen from anthers to stigmas 

 and from plant to plant, thus bringing about a certain amount of cross fer- 

 tilization. Willows and some other dioecious flowers are so fertilized, 

 chiefly by bees. But most insect- visited flowers have the stamens and pis- 

 tils associated either in tke same or in contiguous blossoms. Even when 

 in the same blossom, anthers and stigmas are very commonly so situaW 



