22 INTRODUCTION 



arrangements of flowers considered in relation to actual insect visits, that crossing 

 is absolutely the more advantageous mode of fertilization. If, on the one hand, 

 the experimental method has the advantage of being directly demonstrative, there 

 is, on the other hand, a much larger amount of indirect evidence adducible from 

 the arrangements for pollination. It is, perhaps, hardly more difficult to obtain 

 indirect evidence from a few hundred flowers than to make direct experiments 

 on a few. If by itself, such evidence would scarcely satisfy us, yet it brings 

 complete conviction when considered along with the results of the Darwinian 

 experiments, and takes us even a step further than those experiments. From 

 Darwin's experiments, which lasted eleven years, it is not proved, and perhaps 

 it would not be proved if the experiments lasted a hundred years, whether the 

 capacity of certain flowers to reproduce by spontaneous self-polHnation is limited 

 or unlimited. From the floral arrangements, on the other hand, we can conclude 

 that this capacity must have its limit. For, were it unlimited, cleistogamous flowers 

 would be the most advantageous, and many plants would necessarily have come 

 to possess such flowers only. As a matter of fact, however, not a single plant 

 is known which reproduces itself exclusively by spontaneous self-fertihzation. The 

 investigation of pollination arrangements in connection with actual insect-visits 

 therefore furnishes evidence that is very convincing, even though of secondary 

 nature. It constitutes a no less essendal support of the floral theory than the 

 experimental proof that, as a matter of fact, more vigorous off"spring result from 

 crossing than from self-fertilization.' 



Hermann Miiller's works stimulated many botanists in the most marked way, 

 and a vigour never before manifest became apparent in the field of Flower Pollination. 

 In addition to the older specialists, Darwin, Delpino, Hildebrand, Hermann Miiller, 

 and his brother, who was no less enthusiastic for this science, a number of younger 

 investigators began to apply themselves to this branch, so that a division of labour 

 resulted, and the investigations undertaken in various districts were directed pardy 

 to the extension of the various sections of Flow-er Pollination, partly to an investigation 

 of floral arrangements, and the discovering of the visitors of flowers. Our know- 

 ledge of nectaries^ was extended in Germany by the works of W. J. Behrens; in 

 France by Gaston Bonnier; in North America by Trealease (all 1879). Investigations 

 on stamens were pubfished by Chatin (France), Askenasy, H. Fischer, Oetker 

 (Germany), Bennett (England); on stigmas by J. Reinke, Behrens (Germany), 

 Capus (France); on the processes of fertilization by Dalmer, Strasburger, Elfving, 

 Treub, Juranyi, Goroschankin, Guignard; on the distribution of sexes by Asa 

 Gray, E. Warming, Hackel, Breitenbach, Magnus, Potoni^, Errera and Gevaert, 

 F. Ludwig, Solms-Laubach ; on heterostyly by Breitenbach, Kny, Kohne, W. Burck, 

 Urban, Bailey, Clarke, Meehan, Ernst, Bessey, Battandier, Todd, Knoblauch, Pirotta, 

 Wilson ; on cleistogamy by Ascherson, Potonie, Batalin, Ludwig, Trealease, Heckel, 

 Pringle, Asa Gray, Godron, Hackel, Meehan, Coulter, Graebner, Schroter, Battan- 

 dier, G, M. Thompson, Grisebach, Drude, Kearney, Kohne, Solms-Laubach, Burck ; 

 on pseudo- and hemi-cleistogamy by Fitzgerald, Moore, Reichenbach fil., Freyhold, 



^ Partly taken from Loew: 'Einfuhrting in die Bliitenbiologie,' pp. 291 et seq., and ' Bliiten- 

 biologische Floristik,' pp. 172-5. 



