AUTOGAMY AIDED BY THE COROLLA. 



375 



cium, Leontodon, and Hypochceris, in whose capitula the peripheral ligulate florets 

 are considerably longer than those of the centre, it is easy to see that when the 

 capitula close in the evening the ligulate petal in each flower rises up and lays its 

 inner surface upon the pollen which has been extruded from the tube of anthers in 

 the course of the day. The pollen remains sticking to the petal during the two 

 succeeding days, and in the meanwhile the latter grows about a couple of milli- 

 metres in length and carries the pollen up with it. At the same time the style 

 undergoes elongation and protrudes out of ;,he top of the tube of anthers, holding 

 its two arms, which are now divergent and expose the receptive stigmatic tissue 



Fig. 306. — Autogamy effected by means of the corolla. 



1 PedieularU incarnata, 2 a flower of Pedicularis incamata which has just become accessible to insects, s Longitudinal 

 section through the same flower. * The same flower in a later stage of development. * Longitudinal section through the 

 flower of *. 6 The same flower shortly before the corolla fades; the upper Up is bent down and the mealy pollen falling 

 out of the loosened valves of the anthers is trickling through the tubular upper lip upon the stigma stationed in front of 

 the mouth of the tube. 7 Longitudinal section through the flower of «. 1 nat. size; the other figures double their nat.size. 



upon their surfaces, at the same level as the pollen sticking to the ligulate corolla. 

 When next the capitulum closes, the pollen is transferred to the stigmas, and auto- 

 gamy ensues. This adaptation of the marginal florets of the capitula is all the more 

 interesting, seeing that in the central florets in the same plants, geitonogamy has 

 been found invariably to prevail (c/. p. 319). 



One of the most curious contrivances for efiecting autogamy consists in a special 

 inflection of the corolla, on the termination of the flower's period of bloom, enabling 

 it to conduct the pollen which falls from the anthers to the stigmas. The pollen in 

 these cases is of mealy consistence. Two species of the Lousewort genus (Pedicu- 

 laris) may be used to illustrate this form of adaptation, and we will first take 



