12 THE FERTILISATION OF FLOWERS. [PART I. 
self-fertilisation, which occurs spontaneously in all flowers of this 
plant, is completely inoperative, that even crossing of different 
flowers on the same individual gives a very poor yield, and that 
only the crossing of separate plants results in full produc- 
tiveness. A powerful objection to the Knight-Darwin law 
was removed by this discovery. Finally, in his. Geschlechter- 
Vertheilung bei den Pflanzen (1867), he has striven to show that 
throughout Phanerogams cross-fertilisation of separate individuals 
either takes place in all cases, or does so for the most part, or is at 
least possible; and he has given the following classification of 
phanerogamic flowers according to the comipletendss with which 
they exclude self-fertilisation :— 
A. Male and female organs in different flowers (diclinism). 
Cross-fertilisation ensured, and effected by insects or by the 
wind. Ex. Cannabis, 
B. Male and female organs in one and the same flower (monoclinism). 
1, The organs of the two sexes not developed simultaneously (dichogamy),. 
(a) The male before the female! Ex. Geranium pratense. 
(b) The female before the male? Ex, Luzula pilosa. 
Self-fertilisation usually prevented, and cross-fertilisation 
effected by insects, 
2. The organs of both sexes developed simultaneously (homogamy). 
(a) Flowers expanding ( flores chasmogami, Axell). 
I, Anthers distant from the stigma. 
a. Styles of different lengths on different plants of the same 
species (Heterostyly,, Hild. ; dimorphism and trimorphism, 
Darwin). 
Self-fertilisation not altogether prevented, but either quite 
inoperative (Pulmonaria officinalis) or yielding little 
result (Primula sinensis). 
8. Styles of the same length in all the flowers (Homostyly). 
* Reproductive organs changing their relative positions during 
the flowering period. 
Self-fertilisation avoided, cross fertilisation effected by 
insects. Ex. Anoda hastata. 
** Reproductive organs remain unchanged in position during 
the flowering period. 
+ The aid of insects necessary for fertilisation. 
Self-fertilisation to a great extent impossible, and cross- 
fertilisation necessary. Ex. Orchidacee. Self-fertilisation 
1 Sprengel calls this species of dichogamy, male-female, or dichogamia androgyna ; 
Hildebrand, protandrous ; Delpino, proterandrous. 
R Sprengel calls this species of dichogamy, female-male, or dichogamia gynandra ; 
Hildebrand, protogynous; Delpino, proterogynous. Delpino distinguishes two 
varieties, viz., proterogynia brachybiostigmatica, where the stigmas are short-lived 
and. wither before the anthers ripen; and proterogynia macrobiostigmatica, where 
the stigmas remain capable of fecundation until the anthers are mature, and where 
consequently self-fertilisation remains possible. 
