133 



Hermann Mueller, in giving a general retrospect on the 

 subject of crosS'polliuation, says in regard to self-pollination; 

 "Where cross fertilization that had once been insured be- 

 comes uncertain owing to the competition of other flowers, 

 (e g. Malva rotundifoUa, species of Geranium), or owing to 

 the unfavorable locality (as Lysimachia nemorum) or unfavor- 

 able weather (as Veronica heccahunga), tl)e mechanisms of the 

 ftowers have in many cases undergone a change such as to 

 render self-fertilization again possible; in a few cases rever- 

 sion toanemophily has taken place {Artemisiaceae, Thalictrum). 

 As examples of the countless ways in which plants revert to 

 self-fertilization in default of sufficient insect-visits, I may 

 mention the following: In some dichogamic flowers the 

 stigmas curl back upon the anthers or other parts which still 

 retain some pollen [Stellarm graminea, Malva rotundifoUa, 

 species of Geranium, Compositae); the stigmas sometimes curl 

 back till they come in the line of fall of the pollen [Melam- 

 pyrum pratense) or even place themselves between the anthers 

 {Bhinanthus minor); anthers which stand in a ring around the 

 stigma, may, in default of suflicient insect-visits, converge 

 above the stigma, applying their pollen to it [Myosotis, 

 Lithospermnm, Cruci/erae); even mechanisms which eftect 

 cross-fertilization with astonishing precision in case of insect- 

 visits are not unfrequently transformed so as to render self- 

 fertilization inevitable when insect-visits are few (certain 

 Orchidaceae, Fumariaceae, Salvia); or the production of 

 cleistogamic, self-fertilized flowers may compensate for the 

 loss of the power of self-fertilization in the ordinary flowers 

 {Viola).'' 



Cleistogamous Flowers- The intest in these is cer- 

 tainly to have self-fertilization, and it is remarkable that the 

 closed flowers are very productive of seed, more so than many 



