SEXUAL REPRODUCTION. 155 



with a more than usually divergent life-experience, the reproductive 

 elements which are intermingled have probably a corresponding divergence 

 in chemical constitution. 



The early researches of Kolreuter (1761) gave a firm basis to the study 

 of hybridisation among plants. The comparative easiness of experiment 

 has advanced the botanical side of the subject to far greater certainty than the 

 zoological conclusions can pretend to. Among plants, as we should expect 

 from their greater vegetativeness, the fertility of hybrids seems frequently 

 established. Knight, Gartner, Herbert, Wichura, and others, have 

 brought together a great number of reliable observations, and the 

 whole subject has been admirably discussed by Niigeli. For a copious 

 resume of the general results, for the most part after N'ageli, the student 

 may be referred to chap. vi. of Sachs' Text-book of Botany, while Wallace's 

 " Darwinism" should be consulted for its rediscussion of hybridisation in 

 animals. 



