44 INTRODUCTION 
or five days; in Humulus Lupulus, Mercurialis perennis, and ovata, and others, it 
is at least two days. 
Those plants which bear falsely hermaphrodite flowers behave just like the 
true diclinous plants. Such flowers possess both stamens and pistil, and look 
like genuine hermaphrodites, but either the anthers are degenerate, containing no 
pollen capable of fertilizing (falsely hermaphrodite fruiting-flowers) or the pistil 
does not come to maturity (falsely hermaphrodite pollen-flowers). According to 
Kerner (op. cit., pp. 312-13) various Valerians (Valeriana dioica, polygama, 
tripteris) living in the same localities open their falsely hermaphrodite fruiting- 
flowers three to five days earlier than their falsely hermaphrodite pollen-flowers, 
so that they are markedly protogynous. In Rumex alpinus, the difference amounts 
to two or three days; in Fraxinus excelsior usually to four days, and in numerous 
grasses (Anthoxanthum odoratum, Hierochloa australis, Melica altissima, Sesleria 
coerulea) to two days. 
In Homogamous open flowers cross-pollination is also predominant in most 
cases, at least at first. This is either because the pollen surrounding the stigma 
is ineffective for the fertilization of the same flower (see the list of self-sterile plants, 
p- 36), or the anthers lie, at any rate to begin with, deeper than the stigma (many 
Cruciferae), or they are remote from the stigma (Sileneae), or they turn the 
dehiscent side outwards (many Cruciferae). Numerous interesting cases illustrating 
the impossibility of self-pollination, or at least of its restrictions, are presented by 
the floral adaptations of Orchidaceae, Iridaceae, Violaceae, Ranunculaceae, Labiatae, 
Scrophulariaceae, Boraginaceae, Asclepiadaceae, and Apocynaceae. An account of 
them is impossible here, and reference must be made to the second part of this 
handbook, in which the floral adaptations of individual species are fully described. 
Delpino (‘ Ult. oss.’ Atti Soc. ital. sc. nat., Milano, xvi, pp. 332 et seq.) dis- 
tinguishes four degrees of Herkogamy. 
1. Absolute Herkogamy (Ercogamia assoluta): the transference of pollen 
to the stigma can only be effected by animals; the possibility of self-pollination 
is always excluded. 
2. Contingent Herkogamy (Ercogamia contingente): here, too, the visits of 
insects are necessary for pollination, but accidental self-pollination is not excluded. 
3. Half-Herkogamy (Emiercogamia): the flowers are at first absolutely herko- 
gamous. If there are no insect-visits at this time, self-pollination takes place in 
the second stage of flowering, being rendered possible from growth or change in 
position of the parts of the flower. 
4. Concealed Herkogamy (Ercogamia oscura): the herkogamy is incon- 
spicuous. When insects visit the flowers self-pollination can take place as easily as 
cross-pollination. Failing such visits self-pollination is spontaneously effected. 
V. Heterostyly. 
In speaking of the flowers of Hottonia palustris (‘Entd. Geh., p. 103) 
Sprengel says :—‘ Some plants have only flowers of which the stamens are included 
in the corolla tube, while the style projects from it; and other plants have only 
flowers with the style shorter, but the stamens longer than the corolla tube. 
