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-pollinadon 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. 



