AUTOGAMY THROUGH AGENCY OF COROLLA. 365 



the pollen out of the tube of anthers and leave it in a round lump at the top of the 

 tube (see fig. 303 ^), whence it may be carried off by insects. At this stage the 

 corolla and the hairs of the pappus are 6 mm. long. Soon afterwards the two style- 

 branches, which have undergone rapid elongation, part asunder, and the pollen, if 

 not already removed by insects, is shaken off, and falls on to the pappus-hairs, 

 where it is caught by the asperities on their surfaces (see fig. 303 ^). The receptive 

 tissue on the inner faces of the style-branches, which are now the upper surfaces, 

 are in a position to get dusted with pollen brought by insects from other flowers. 

 Meanwhile an elongation of every part of the flower has taken place; the pappus- 

 hairs have attained a length of 7 mm., and the corolla of 6-5 mm. Lastly, the 

 flower enters upon its third stage of development. The two style-branches curve 

 down, bringing the stigmatic tissue into contact with the pollen sticking to the 

 pappus-hairs, which have by that time grown another millimetre, and are therefore 

 reached all the more easily, as they even project above the arms of the style (see 

 figs. 303 9 and 303 ^«). 



In all the cases hitherto dealt with the only parts of the flower which are con- 

 cerned in bringing about autogamy are the stamens and pistils. The filaments in 

 some instances, the parts bearing stigmatic tissue in others, undergo inclination or 

 inflection, whilst sometimes both organs mutually approach one another. No direct 

 part in the process of autogamy is taken in any of these plants by the whorls of 

 petals surrounding the stamens. We will now proceed to describe cases in which 

 I the petals are instrumental in effecting self-fertilization. 



I The simplest case of the discharge of this function by petals is to be found in 



I flowers which are in the shape of tubes, cups, or basins, and whose anthers are 



adnate to the inner surfaces of the petals, and are brought into contact with the 



stigma in consequence of a contraction or closing together of the corolla — Thymelcea 



Passerina, a low shrub belonging to the Thymelacese, will serve as an example. 



j The small inconspicuous flowers of this species contain nectar, and by its perfume 



I attract insects which brush pollen from the anthers as they suck the honey and 



i convey it to the stigmas of other flowers. The anthers are adnate to the inner face 



I of the cup-shaped perianth, and are at first at a distance of only i mm. from the 



{ stigmas. Notwithstanding this proximity the viscid pollen is not spontaneously 



' transferred to the adjacent stigma when the flower is first open. It is not till the 



flower is nearly over that a slight contraction of the upper third of the perianth 



causes the anthers to be pressed against the stigma, which stands at the same level 



IS themselves. In Claytonia perfoliata, one of the Portulace^e, autogamy is effected 



i in the same manner, the only difference being that the anthers are borne on special 



' fihform filaments which are adnate to the bases of the petals. These filaments, 



however, share in all the petals' movements, and the anthers at their extremities 



are pressed exactly upon the stigma when the corolla closes up. 



In other cases the epipetalous stamens hold their anthers at the commencement 

 of the flowering period underneath or behind the stigmas, and are pushed upwards 

 during the flowering period by an elongation of the petals, in consequence of which 



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