8l2 



PHENOMENA OF SEXUAL REPRODUCTION. 



become attached to its hairs, feet, or proboscis, and afterwards, when assuming similar 

 positions, to be applied to the stigmas of other flowers. In dichogamous plants the 

 movements of the stamens, styles, or arms of the stigmas assist this end, taking place 

 frequently in such a way that at one time the open anthers occupy the same position 

 in the flower that the receptive stigmas do at another time, so that the insect, when 

 taking up the same position, touches the open anthers in one flower and the receptive 

 stigmas in another flower with the same part of its body. The same result is also ob- 

 tained in dimorphic flowers, the pollination being in these cases efficacious when anthers 



l-'IG. a,-^-j.—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. 458. — Arisiolochia Ckj>iatitis : \\\ perianth cut 

 through longitudinally. A before, B after pollination 

 (magnified). 



and stigmas which occupy the same position in different flowers are made mutually to 

 act on one another. But there are besides many other contrivances, most variable in 

 their nature and often perfectly astonishing, for effecting the conveyance of pollen by 

 insects. A few examples may suffice. 



(i) Dichogamous Flowers^ are oxWi^x protandrous oy 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 



^ F. Delpino, Ulteriori osservazioni sulla dicogamia nel regno vegetabili, 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.— Ed.] 



