910 PHENOMENA OF SEXUAL REPRODUCTION. 
(i) Dichogamous Flowers^ are either protandrous 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, 
Campanulaceae, Labiatse, Digitalis, Sec. The phenomena referred to, especially the 
movements of the stamens and stigmas, are so readily observed in these cases, e.g. in 
Geranium and Althaea, that no further description is necessary. In protogynous flowers 
Fig. 489. — Aristolochia Cleinatitis : the perianth cut 
through longitudinally. 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 sei. 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 'synacraic' 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.] 
