20 THE BOOK OF NATURE STUDY 



straightening of the style, and projects in the centre of the flower 

 (Fig. 5, 3) with the stigmatic lobes widely expanded. When the 

 flowering is over the open stigma is again moved downwards by 

 the bending of the style. 



The way in which the flower works as an arrangement to 

 prevent self-pollination, and to ensure cross-pollination, when 

 visited by insects, will now be easily understood. The mechanism 

 is of special interest, as having been carefully studied by Sprengel, 

 the first thorough investigator of the relations of insects and 

 flowers. The conspicuous flowers grouped in large prominent in- 

 florescences are highly attractive to insects, and offer an abundant 

 secretion of nectar. Insects of various kinds visit the flowers, 

 but bees are the most numerous. In flowers in the earlier stage, 

 the stamens, some of which will be shedding their pollen, project 

 and form a convenient alighting place. The insect will thus get 

 the under surface of its body smeared with pollen as it inserts 

 its proboscis between the stamens to get at the nectar. It cannot 

 possibly place pollen on the stigma of the same flower, since this 

 is closed. On passing, however, to a flower in the later stage on 

 the same or another inflorescence the open stigma projecting in 

 the place previously occupied by the stamens will prove the 

 suitable alighting place, while the stamens are now bent aside. 

 Any pollen derived from flowers in the earlier stage will thus be 

 rubbed on the stigma, and cross-pollination be effected. 



The inferior ovary, as might be inferred from the four-lobed 

 stigma, is formed of four carpels, and encloses four cavities in each 

 of which are numerous ovules (Fig. 5, 8). After pollination the 

 sepals, petals, stamens, and style all fall off, and the inferior ovary 

 enlarges to form the fruit (Fig. 5, 7). This has numerous seeds 

 closely packed together in its four long narrow cavities. When 

 mature, the fruit opens by the wall splitting away as four valves 

 from a central column (Fig. 5, 9). The seed itself is brownish, 

 and has a smooth coat enclosing the small embryo plant. It has 

 a crown of fine white silky hairs (Fig. 5, 10, u) which spread out 

 and form a parachute, assisting in the dispersion of the seeds by 

 the wind. 



The similarity of the seeds of Epilobium to those of the Willow 

 accounts for the name Willow-Herb given to the plant we are 



