36 INTRODUCTION 



19. Autogamy by correlated curving of the flower-stalk, and elongation of the 

 petals' : Pulsatilla vulgaris and vernalis. 



20. Autogamy by correlated curving of the flower-stalk, lengthening of the 

 petals, lengthening of the stamens, and curving of the style : Geum rivale ; Rubus 

 Idaeus and some related forms. 



The effect of the pollen on the stigma of the same flower is very varied. 

 There are numerous cases known in which it is absolutely inactive {^self-sterility), 

 but in still more numerous instances there is no considerable difference between 

 the effect of pollen of the same plant, and foreign pollen {self-fertility). If pollen 

 from the same plant and pollen from another plant get to the stigma, it has 

 been proved in many cases that the latter is more effective than the former — i.e. 

 the foreign pollen predominates or is prepotent. 



The investigations of different observers with regard to the self-sterility and 

 self-fertility of many plants have not infrequently given contradictory results. Thus, 

 for example, according to Hildebrand and Kirchner, rape (Brassica Rapa) is 

 self-fertile, while, according to Lund, Kjaerskou, and Focke, it is self-sterile, 

 so that we must assume that self-sterility is a character that is not constant for 

 all individuals of the same species, but varies with the locality and the individual. 



The best-known cases of Self- sterility or infertility of a plant as regards 

 its own pollen are as follows : — 



Ranunculaceae. — Ranunculus acris (Focke), perhaps also R, bulbosus (Focke). 

 Nigella damascena (Hoffmann). Delphinium Consolida (Darwin). 



Papaveraceae. — Cultivated specimens of Papaver alpinum (H. Hoffmann), 

 P. Rhoeas (Hoffmann), P. somniferum (Hoffmann), P. nudicaule (Focke). Esch- 

 scholtzia californica (Fr. MflUer, Chas. Darwin). Hypecoum grandiflorum 

 (Hildebrand). 



Fumariaceae. — Dielytra spectabilis (Delpino). Corydalis cava and solida 

 (Hildebrand). 



Cruciferae. — Brassica Rapa (Focke, Lund, and Kjaerskou). Raphanistrum 

 arvense (Hoffmann). Dentaria bulbifera (Delpino, Knuth). 



Cistaceae. — Hybrid forms of Cistus (Bomet). 



Violaceae. — Large -flowered specimens of Viola tricolor (Hermann Miiller), 

 V. canina (Darwin). 



Silenaceae. — Dianthus Caryophyllus (Darwin). 



Resedaceae. — Some specimens of Reseda odorata (Darwin), and of R. lutea 

 (Darwin, Focke). 



Malvaceae. — Abutilon Darwinii Hook. (Fritz Miiller, Darwin), A. striatum 

 Dicks., A. venosum Hook., A. forma hybr. (Fr. Mailer). 



Geraniaceae. — Erodium macradenum(Fr.Ludwig). Pelargonium zonale (Darwin). 



Onagraciae. — Sp. of Fuchsia (Gartner). 



Lyihraceae. — Cuphea purpurea (Gartner). 



Melastomaceae. — Centradenia floribunda, Rhexia glandulosa, Pleroma, Mono- 

 chaetum ensiferum, Heterocentron mexicanum (Darwin). 



Rosaceae. — Rubus odoratus and spectabilis (Focke). Kerria japonica and 

 Neviusia alabamensis in Europe (Focke). 



