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 (se//sterility), 
but in still more numerous instances there is no considerable difference between 
the effect of pollen of the same plant, and foreign pollen (se/Afert:lity). 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, Kjerskou, 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. Miiller, Chas. Darwin). Hypecoum  grandiflorum 
(Hildebrand). 
Fumariaceae.—Dielytra spectabilis (Delpino). Corydalis cava and solida 
(Hildebrand). 
Cruciferae.—Brassica Rapa (Focke, Lund, and Kjerskou). Raphanistrum 
arvense (Hoffmann). Dentaria bulbifera (Delpino, Knuth). 
Cistaceae.— Hybrid forms of Cistus (Bornet). 
Violaceae.— Large-flowered specimens of Viola tricolor (Hermann Miller), 
V. canina (Darwin). 
Stlenaceae.— 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 fook., A. forma hybr. (Fr. Miller). 
Gerantaceae—Erodium macradenum (Fr. Ludwig). Pelargonium zonale(Darwin). 
Onagraciae.—Sp. of Fuchsia (Gartner). 
Lythraceae.—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). 
