THE DICOTYLEDONES 



1783 



the style. Where the style leaves this cone it is covered with hairs which 

 prevent the entry of rain, though the proboscis of an insect can push 

 between them. In the young flowers the stamens are covered with pollen 

 grains which are bound together by viscid threads. These stamens bend 

 outwards and permit insects to alight on them (Fig. 1674). Later the 

 dehisced stamens curve downwards, while the style, which at fi.rst is quite 



B 



Fig. 1674. — Epilobium hirsntiim. Three successive stages in anthesis. A, Stamens spreading, 

 stigmas still immature. B, Stigmas expanded, above the level of the stamens. C, Stigmas 

 recurved. Self-pollination is now possible. 



short, now elongates and four divergent stigmas are produced which form 

 the only alighting place for visiting insects. Hence insects coming from 

 younger flowers will pollinate the stigmas with pollen borne mainly on 

 their feet. 



\n Epilobium hirsutum the flowers vary somewhat in size; in the large- 

 flowered forms the stamens ripen first and the style is long and curved in 

 such a way that self-pollination is impossible. In medium-sized flowers, 

 both the style and stigmas ripen at the same time, the style is straight and 

 should insect visits fail, the stigmas bend back so that they touch the anthers 

 of the longest stamens, making self-pollination possible. In the small 

 flowers the stigmas are produced at the same level as the longest stamens 

 and automatic self-pollination is almost inevitable. 



Finally in Epilobium parviflorum the flowers are quite small and are 

 rarely visited by insects. Four of the stamens are longer and four shorter 

 than the style. An insect visiting the flower may effect cross-pollination, 

 but if that fails the style is almost certain to receive pollen from the shorter 

 stamens. This condition is similar to that in E. collinutn in which automatic 

 self-pollination inevitably occurs on the first day of anthesis, the stamens 

 being of a length suitable for the anthers to touch the stigmas. 



The seeds of the Willow-herbs are characterized by a group of long 

 hairs which develop from the chalazal end of the seed. These plumed 

 seeds are liberated successively from the capsule and ensure a very wide 



2A* 



