9TO 



PHENOMENA OF SEXUAL REPRODUCTION. 



(i) Dichogamous Flowers^ are either protnnclrous or protogynous"^. In the former the 

 stamens are developed first, their anthers opening at a time when the stigmas are still 

 undeveloped and not yet receptive ; the stigmatic surface is only developed later, and 

 usually not till the pollen has been carried away from the anthers by insects ; they can 

 then only be fertilised by the pollen of younger flowers. To this category belong the 

 various species of Geranium, Pelargonium, Epilobium, Mal'va, Umbelliferae, Compositae, 

 Gampanulaceae, Labiatae, Digitalis, &c. The phenomena referred to, especially the 

 movements of the stamens and stigmas, are so readily observed in these cases, e.g. in 

 Geranium and jilthooa, that no further description is necessary. In protogynous flowers 



Fig. 4,W.—Aristolochia Clematitis: a piece of a stem st with 

 petiole b ; in the axil of this are flowers of different ages ; i, i 

 young flowers not yet fertilised ; 2, 2 fertilised flowers, the pedicels 

 bent downwards ; k swollen part of the tube of the perianth r ; y the 

 inferior ovary (natural size). 



Fig. 489. — Aristolochia Clematitis: the perianth cut 

 through longhudinally. A before, B after pollination 

 (magnified). 



the stigma is receptive before the anthers in the same flower are mature ; when these 

 subsequently open and allow the pollen to escape, the stigma has already been pollinated 

 by foreign pollen or has even withered up and fallen off (as in Parietaria diffusa) ; and 

 the pollen of these flowers can therefore only be applied to the fertilisation of younger 



^ F. Delpino, Ulteriori osservazioni sulla dicogamia nel regno vegetabile, Atti della soc. Ital. 

 di sci. nat. vol. XIII, 1869, and Bot. Zeit. 1871, No. 26 et seq. ; ditto, in Bot. Zeit. 1869, p. 792. 



^ [For a list of British protandrous, protogynous, and 'synacmic' plants (or those in which the 

 male and female organs are mature at nearly the same time), see A. W. Bennett in Journal of 

 Botany, 1870, p. 315, and 1873, p. 329.] 



