114 PROTECTION OF POLLEN. 



in the evening grow much larger in the course of the flowering period. In many 

 species they become double as long as they were at the moment the flower first 

 opened. The enlargement of the petals takes place pari passu with certain pro- 

 cesses in the development of the anthers to be protected. Some Ranunculacese 

 with erect flowers — e.g. the Hepatica (AneTnone Hepatica) and Winter Aconite 

 {Eranthis, cf. figs. 222 " and 222 '") — have their pistils surrounded by a crowd 

 of stamens, and these again encircled by concave perianth leaves (petaloid sepals) 

 which are wide open by day but closed at sunset, forming a dome over the stamens. 

 The anthers of these plants do not open simultaneously, but only by degrees. 

 The pollen on the outermost anthers nearest to the sepals is set free first of all, 

 and this happens at a time when the filaments bearing those anthers are still 

 short. It is obvious that comparatively short sepals suffice to shelter these 

 stamens. Gradually, however, the anthers nearer the middle of the flower open; 

 their filaments elongate, and the sepals would now be no longer of sufficient 

 size to form a dome over all the pollen-laden anthers at night time. They 

 accordingly grow in length day by day, until the anthers next to the carpels 

 yield up their pollen. In the case of Eranthis the sepals lengthen in this way 

 from 11 to 22 millimetres (cf. figs. 222^ and 222'°), and in that of Anemone 

 Hepatica from 6 to 13 millimetres; that is to say, they actually double their 

 original length. 



A curious instance of the closing of petals is that of Esckscholtzia Galifornica 

 {cf. figs. 2221 g^jj^ 222^). By day the four golden-yellow petals are expanded, 

 the pollen falls from the stamens, which grow in a bunch in the middle of the 

 flower, on to the concave petals, and rests on them in a floury layer as much as 

 1 millimetre in depth. When evening comes the anthers in the centre, having 

 already lost their pollen, are left unprotected, but each petal furls itself up 

 longitudinally in the prettiest manner conceivable, and thus the fallen pollen is 

 sheltered under four little tents. 



The flowers composing the capitula of the Dandelion (Taraxacv/m), Lettuce 

 {Lactuca), Chicory (Gichorivmi), Nipple-wort {Lapsana), and many other Com- 

 posites, of which we may here select the Mouse-ear Hawkweed (Hieracium 

 Pilosella (fig. 222) as type, have tubular bases, but above are produced unilaterally 

 into a strap-shaped structure to which the term ligule is applied. From the 

 bottom of each ligulate flower spring flve stamens whose anthers are connate 

 into a tube. This tube is early filled with pollen discharged introrsely, i.e. 

 towards the centre of the flower through longitudinal slits in the anthers. The 

 style is embedded in the tube, and as soon as the pollen is liberated it elongates, 

 and, acting like a chimney-sweep's brush, pushes up the pollen which fills the 

 anther-tube until it rests above the opening at the top. The pollen resting on 

 the top of the style is brushed off by insects when they settle upon the capitula. 

 But it is not certain that insects will make their appearance within a few hours 

 of the extrusion of the pollen, and even if they do they only brush lightly over 

 the flowers, and are sure to leave some of the pollen behind, and this pollen is 



