i.] CROSS-FERTILIZATION. 3 



Mr. Darwin, however, has not only made it clear 

 from theoretical considerations, but has also proved it, 

 in a variety of cases, by actual experiment. More re- 

 cently Fritz Miiller has even shown that in some cases 

 pollen, if placed on the stigma of the same flower, has 

 no more effect than so much inorganic dust ; while, and 

 this is perhaps even more extraordinary, in others the 

 pollen placed on the stigma of the same flower acted 

 on it like a poison. This he observed in several species ; 

 the flowers faded and fell off, the pollen masses them- 

 selves, and the stigma in contact with them shrivelled 

 up, turned brown, and decayed; while flowers on the 

 same bunch, which were left unfertilized, retained their 

 freshness. 



The importance of this "cross-fertilization," as it 

 may be called, in contradistinction to " self-fertiliza- 

 tion," was first conclusively proved by Mr. Darwin in 

 his remarkable memoir on Primula (Linnean Journal, 

 1862), and he has since illustrated the same rule 

 by researches on Orchids, Linum, Lythrum, and a 

 variety of other plants. The new impulse -thus given 

 to the study of flowers has been followed up in this 

 country by Hooker, Ogle, Bennett, and other naturalists, 

 and on the Continent by Axell, Delpino, Hildebrand, 

 Kerner, F. Miiller, and especially by Dr. H. Miiller, 

 who has published two excellent works on the subject, 

 bringing together the observations of others, and adding 

 to them an immense number of his own. 



In by far the majority of cases, the relation between 

 flowers and insects is one of mutual advantage. In 

 some plants, however, as for instance in our Common 

 Drosera, we find a very different state of things, and 



B 2 



