HTBEIDIZATIOX. 779" 



Kucleus or Kernel, p. 333 ; and Development of the Embryo, p. 

 336.) 



Mr. Darwin has shown that, in numerous plants, crossing is 

 necessary for a completely fertile union of the sexes ; that is, 

 that the ovules of one flower must be fertilized by pollen from 

 another. This may be effected in many ways ; e.g. by the wind 

 in dioecious plants, or frequently by the unconscious agency of 

 insects, as in the Orchidacecs, where the various modifications 

 of structure to ensure cross-fertilization by this latter means 

 are strikingly beautiful. It seems not unlikely that further 

 investigations will prove that self-fertilization is exceptional in 

 plants ; certainly occasional crossing seems to be necessary. 



jDimorphic species are those which possess two forms of both 

 sorts of sexual organs, as species of Priinula, Oxalis, and Pul- 

 monaria, which have both long and short stamens, and long and 

 short styles. The long stamens are associated with the short 

 styles and vice versa, in the flowers ; and Mr. Darwin has- 

 proved, by experiment, that, for the complete fertilization of 

 either kind of pistil, it is necessary that pollen from the stamens 

 of corresponding length, and therefore from a different flower, 

 be employed. Lythrum Salicaria is trimorphic, and similar laws 

 have been observed to prevail in its fertilization. 



Hybridization, Hybridation, or the Production of Hybrids in 

 Plants. — If the pollen of one species is applied to the stigma of 

 another species of the same genus, should impregnation take 

 place, the seeds thus produced will give rise to offspring inter- 

 mediate in their characters between the two parents. Such 

 plants are called hybrids or mules. The true hybrids, which are 

 thus produced between species of the same genus, must not be 

 confounded with simple cross-breeds, which result from the 

 crossing of two varieties of the same species ; these may be 

 termed sub-hybrids. 



As a general rule, true hybrids can only be produced between 

 nearly allied species, although a few exceptions occur, where 

 hybrids have been formed between alhed genera ; these are called 

 higeners. The latter, however, are not so permanent as the 

 former, for in almost all cases they are short-lived. 



Hybrids always possess some of the characters of both parents, 

 but they generally bear more resemblance to one than the other. 

 Sometimes the influence of the male parent is most evident, and 

 at other times that of the female, but no law can at present be 

 laid down with regard to the kinds of influence exerted by the 

 two parents respectively in determining the characters of the 

 hybrid. In very rare cases, it has been noticed, that different 

 shoots of the same hybrid plant have exhibited different charac- 

 ters, some bearing flowers and leaves like their male parent, 

 others like the female, and some having the characters of both. 

 In such cases, therefore, the hybrid characters are more or less 



