n 



360 AUTOGAMY. 



branches below the sweeping-hairs, and may be recognized by the granulated 

 .appearance of its turgescent cells. The behaviour of the stylar branches from the 

 commencement to the termination of a flower's bloom is shown in fig. 302 \ where 

 the three tubular florets are in successive stages of development. Almost simul- 

 taneously with the opening of the tubular corolla the two style-branches are pushed 

 up above the anther-tube, and the poUen is swept out of the tube by the hairs pre- 

 viously referred to. The style-branches at this period are in close contact, and the 

 receptive tissue of the stigmas is not yet accessible (fig. 302 \ left-hand fioret). 



Fig. 302.— Autogamy by means of a crossing or a bending back of the style-branches. 



^ Aster alpinus. Portion of a eapitulum, including a marginal female floret with ligulate corolla and three tubular florets of 

 the disc. The latter are in the successive stages which lead to autogamy (left to right). ^ Style-branches of Aster al^invx 

 which have just separated but still have some pollen clinging to their hairs. 8 The style-branches crossed so as to transfer 

 the pollen from the collecting-hairs of the one to the stigmatic tissue of the other. *, ^, ^ Florets from the centre of a 

 eapitulum of Centaurea rntrntana in successive stages leading to autogamy. 7 The two style-branches rolled back suffi- 

 ciently to bring the stigmatic tissue into contact with the pollen gn the collecting-hairs. & CwmpanuLa persic^olia; 

 longitudinal section through a newly-opened flower. 9 xhe same with the style-branches rolled back so as to bring the 

 stigmatic tissue into contact with the pollen on the exterior surface of the stylar column. " Flower of Phyteuma orbictdare 

 in process of transition from the flrst to the second stage of development. " The same flower in the last stage of develop- 

 ment. ', ' natural size ; the rest magnified. 



Neither cross- nor self-fertilization of the flower in question can at present be 

 •efiected, and the pollen is only exposed that it may be carried away by insects to 

 fertilize other blossoms. The two style-branches are subsequently lifted still 

 higher and move a little apart, with the result that the pollen clinging to their 

 hairs, if not already removed by insects, is for the most part pushed oS, falls down, 

 a.nd is appropriated to the purpose of geitonogamy (see p. 321). A small remnant of 

 pollen is, however, invariably left hanging to the lower collecting-hairs, and this it 



