398 AUTOGAMY. 



style does not project outside the throat, and its stigma rests only just above the 

 tips of the anthers. Under these conditions cross-pollination is as likely to be 

 brought about through insect-agency as it is in the case of the long-styled flowers; 

 but in addition autogamy takes place towards the end of the period of bloom. The 

 manner in which the latter is effected is as follows: During the period of the 

 flower's bloom the corolla-tube grows some millimetres in length until finally the 

 ring of anthers, which are adnate to the throat of the corolla, is brought up to the 

 same level as the stigma. The stigma then stands in the centre of the ring and 

 receives an abundant supply of pollen from the adjacent anthers. 



In Primula minima (see figs. 288 x and 288 2 , p. 302) the heterostyled flowers 

 are erect and maintain this position unaltered till the corolla withers. The limb of 

 the corolla in the long-styled form (see fig. 288 x ) is larger than it is in the short- 

 styled form. The anthers in the long-styled flower are inserted on the lower part 

 of the tube; the style projects above the ring of anthers and the stigma rests some- 

 where in the uppermost third of the tube. On entering a flower an insect would 

 first come against the stigma, and would then probably dust it with foreign pollen. 

 Autogamy scarcely ever takes place. In the wild state of the plant the corolla 

 withers without falling off; only in rare instances does it happen that the corolla 

 becomes detached from the receptacle, and is carried away by the wind. On such 

 an occasion the stigma might touch the ring of anthers and get covered with pollen. 

 Self-fertilization is, on the other hand, all the more carefully ensured in the short- 

 styled flowers. Here the anthers are attached to the highest third of the corolla - 

 tube, and the stigma capping the short style rests below the ring of anthers. When 

 the flower's period of bloom is nearly at an end both the corolla-tube and the anthers 

 begin to wither and contract, with the result that the pollen falls from the anthers 

 down the tube, and is caught upon the stigma. 



Thus, autogamy is effected in the long-styled flowers of Primula Auricula and 

 P. glutinosa by the stigma being dragged through the ring of anthers as the corolla 

 falls off, in the short-styled flowers of Primula longiflora by the elongation of the 

 corolla-tube and elevation of the anthers to the level of the stigma, and in the short- 

 styled flowers of Primula minima by the anthers shrivelling and letting their 

 pollen fall. The fact of the occurrence amongst Primulas alone of three kinds of 



*- O 



contrivance for promoting autogamy gives us some idea of the immense variety 

 which prevails in this respect amongst heterostyled plants in general. The impos- 

 sibility of entering here into the further details of this subject is the less to be 

 regretted, seeing that to a great extent such an account would involve a repetition 

 of facts which have already been stated. 



The number of species possessing heterostyled flowers is far larger than was 

 formerly supposed. The list of such species known at the present day includes 

 members of the following families: Boraginacese, Caprifoliaceae, Caryophyllacese, 

 Colchicaceae, Crassulaceae, Ericaceae, Gentianacese, Globulariaceae, Iridacese, Linacese, 

 Lythracese, Onagraceae, Oxalidacese, Papaveraceae, Plantaginaceae, Plumbaginaceae, 

 Polygonaceae, Primulaceae, Rubiaceae, Santalaceae, Solanaceae, and Valerianaceae, and 



