HISTORICAL DEVELOPMENT OF FLOWER POLLINATION 11 
of Friedrich Hildebrand’, which appeared in 1867: ‘ Die Geschlechtverteilung bei 
den Pflanzen.’ In this (pp. 72, 80) Hildebrand gave a classification of the floral 
arrangements known up to his time, as shown in the following summary :— 
A. Male and female organs separate and in different flowers (dicliny) ; cross- 
pollination by wind or insects necessary (Cannabis). 
B. Male and female organs in the same flower (monocliny). 
I. The two sexes developed successively (dichogamy); self-pollination pre- 
vented in nature; cross-pollination by insects or wind. 
(a) The male sex matured before the female (profandrous dichogamy ; 
Geranium pratense). 
(4) The female matured before the male (frofogynous dichogamy; Luzula 
pilosa). 
II. Both sexes developed at the same time (adichogamy). 
(a) Flowers that open (chasmogamy, according to Axell). 
1. Anthers remote from the stigma. 
(a) The proportion between the length of the style and the length of the 
filaments varies in different plants of the same species (heferostyly) ; 
self-pollination is not prevented, but is either entirely without result 
(Pulmonaria officinalis), or is only slightly productive (Primula sinensis). 
a. Two forms of flowers (dimorphism, Darwin). 
8. Three forms of flowers (trimorphism, Darwin). 
(b) The proportion between the length of the style and the length of the 
filaments is the same in all flowers (Aomostyly). 
a. Sexual organs vary during the period of flowering as to their relative 
positions (motion-dichogamy); self-pollination avoided; cross-pollina- 
tion by insects favoured (Anoda hastata, Salvia, &c.). 
8. Sexual organs occupy the same relative positions throughout the 
period of flowering. 
(a) Insect-help essential for pollination. 
* Cross-pollination necessary; self-pollination by insects impossible, 
or at least very difficult (Orchids). 
** Cross-pollination possible; self-pollination to some extent possible, 
but not necessary (Asclepiadaceae). 
(8) Insect-help not essential for pollination; self-pollination possible, 
but cross-pollination by insects also occurs (Vitis, Convallaria). 
2. Anthers applied to the stigma, self-pollination therefore inevitable. 
(a) Fruit not forming without cross-pollination, which is possible only 
through the agency of insects (Corydalis cava). 
(b) Formation of fruit even without cross-pollination ; cross-pollination by 
insects not however excluded (Linum usitatissimum). 
(6) Flowers that never open (c/eisfogamy, Kuhn); only self-pollination possible, 
cross-pollination excluded. In addition to these cleistogamous flowers 
the plant possesses others that open, and accordingly are liable to cross- 
pollination (Oxalis Acetosella). 
1 Professor in Freiburg i. b. 
