PHYSIOLOGY 



313 



gynodujecious and gynomonoecious forms. In the latter the female flowers are 

 borne on the same individual as the hermaphrodite flowers (Aesculus, etc.) ; in 

 the former they are on distinct individuals 

 (Silene inflata, Erodium cicutarium, Satureja). 



Hybridisation. The union of two 

 sexual cells is, as a rule, only possible 

 when they are derived from individuals 

 of the same species ; it is only then that 

 they exercise an attractive influence upon 

 each other and fuse together in the act 

 of sexual reproduction. The sexual cells 

 of Mosses and Ferns, apart from all other 

 considerations, would not unite because 

 the spermatozoids of Mosses are attracted 

 to the female organs by sugar, while 

 those of the Ferns are stimulated by 

 malic acid. In the case of Phanero- 

 gams, a mixed union of sexual cells is 

 likewise prevented by various obstacles 

 to pollination and fertilisation. Oc- 

 casionally, however, the sexual cells of 

 different varieties, species, or even genera 

 have shown themselves able to unite 

 and produce descendants capable of 

 development. Such a union is termed 

 HYBRIDISATION, or bastard -formation, and its products HYBRIDS or 



BASTARDS. 



Through the demonstration of the possibility of hybridisation, 

 the sexuality of plants, for a long time doubted, was indisputably 

 proven. With this object in view, and following the work of 

 FAIRCHILD, in 1717, hybrids were raised in great numbers by 

 KOLREUTER as early as 1761 ( 117 ). It also demonstrated that the 

 real purpose of sexual union was the combination of the properties 

 of both parents, for transitional forms are found among hybrids 

 which in many characteristics resemble the male and in others 

 the female ancestor (heterodynamic hybrids), or they may show an 

 equal combination of the characters of both (homodynamic hybrids, 

 e.g. Nicotiana rustica 9 * Nic. paniculata <$ ). Less frequently it 

 happens that the hybrid resembles one ancestor almost exclusively. 

 In such a case the attributes of the other ancestor remain latent, and 

 may appear regularly or quite unexpectedly, through atavism (p. 

 299), in later generations. 



The mingling of characters is often complete. Had one species simple leaves 

 and the other compound, their hybrid would have leaves more or less cleft ; or 

 were the flowers of one parent species red and those of the other yellow, tin- 

 hybrid frequently bore flowers with red and yellow markings (mosaic hybrids), or 



;. 'J4"). A small inflorescence of 

 Kalmia glauca ; the stamens are re- 

 tained in pocket-like depressions of 

 the corolla. 



