328 CHAPTERS ON EVOLUTION. 



(Fig. 228), sweetwilliam, and allied plants, and by many plants of the 

 daisy and dandelion type (Composite). The latter case (of the earlier 

 ripening of the pistil) is illustrated by the rib-grass (Plantago) of the 

 roadsides, by the cuckoo pint (Arum, Fig. 227), and other plants. 

 One or two familiar illustrations will suffice to show how clearly and 

 effectually nature carries out her intention of securing cross -fertilisa- 

 tion by different periods of ripening in stamens and pistils. 



The pink, or carnation (Fig. 228), in its first condition, exhibits the 

 case of a plant possessing stamens alone. These organs ripen, discharge 

 their pollen (which is carried by insects to flowers whose pistil may 

 then be ripe), and then die away. After the stamens, and with them all 

 chances of self- fertilisation, have disappeared, the pistil matures, and 

 its style and stigma develop fully (Fig. 228). It is then fertilised by 

 foreign pollen that is, by pollen from a pink whose stamens are at 

 that period in full development. So also is it with thyme, whose stamens 

 ripen first ; and with the Canterbury bells, harebells, and like flowers. 

 In the campanulas (Fig. 214) anthers and pistil are closely related 

 before the flower opens ; and when the anthers discharge their pollen, 

 it is shed upon the style or stalk of the pistil ; and only after the 

 stamens have shrivelled up and their pollen has been carried away 

 by insect agency to other "bell-flowers," does the pistil develop 

 fully, and its three conspicuous stigmas open out so as to receive 

 pollen from another and, at that period, pollen-producing flower. In 

 cases like the preceding, therefore, it is evident nature does not 

 intend that the flower's own pollen should fertilise its ovules. 



The opposite case occurs in the Plantago, where the elegant little 

 pistils ripen first, and where the stamens do not mature until fertilisa- 

 tion of their flower has been accomplished by foreign pollen. In the 

 cuckoo pint (Arum, Fig. 227) there is also witnessed the ripening of 

 the pistil before the stamens. Every one knows this plant, with its 

 sheathing leaf (a), and the central stalk (b) bearing the " flowers." 

 The anthers are placed above the stigmas ; hence it would seem, at 

 first sight, as if nature intended that their pollen should fall downwards 

 and fertilise the plant's own ovules. But the pistils ripen long before 

 the stamens. When the latter are mature, the pistil has been already fer- 

 tilised. Hence the pollen, it is evident, must be intended for fertilising 

 other pistils of the species, unless, indeed, we can maintain that 

 nature, like Homer, " sometimes nods." The pollen in this case falls 

 to the bottom of the sheathing leaf, where it might well seem to be 

 lost entirely to the outer world. Small insects, however, in due 

 course arrive upon the scene. Entering the cavity of the leaf readily 

 enough, on the principle Qifacilis descensus Avernt, they find the reverse 

 process, revocare gradum, to be impossible. By an arrangement of stiff 

 hairs, pointing downwards, which they readily enough brush aside on 

 entering, they are prevented from escaping out of the flower. Hemmed 



