154 THE VEGETATIVE ORGANS 



flowers of the Evening Primrose as they open on a warm 



summer's evening. Fig. ioo shows the stages observed 



in two flowers. The calyx slips down on one side and the 



four free tips curve back and reveal the rolled-up petals. 



The corolla unscrews at the base, causes the calyx to split 



more and more, and as the petals unroll, the mouth of the 



corolla opens and the stigmas appear. The calyx now 



splits at the bottom, the sepals suddenly turn backward, 



or inside out, with a distinctly audible click, and the 



crinkled petals unroll, slide over one another, and soon fully 



expand. The sound produced resembles that of two sheets 



of paper, one gliding over the other. If we look at the 



stamens we find that the stringy pollen is already hanging 



out of the anthers, while the stigmas, not yet ripe, spread 



out their four lobes well above them. As many as a dozen 



flowers may be seen to open in this way on one plant in 



half an hour. 



The various attitudes that flowers assume should be 



carefully observed under the following conditions : (i) in 



bud, (2) in flower, (3) in sunshine, (4) in cloudy and wet 



weather, (5) during the day, (6) at night, (7) as the fruit 



ripens, and (8) when the fruit is ripe. Figs. 101 and 102 



show the movements of the flowers and fruits of the Wild 



Hyacinth. Notice that the flowers are erect in bud ; later 



they turn away from the axis, expand and hang downwards, 



the lowest and oldest opening first. After pollination they 



become erect again, while the fruit-stalk lengthens and 



becomes rigid. In the White Clover (see Fig. 98), the 



flowers are erect in bud, horizontal in flower, and after 



fertilization hang downwards. The Wood Sorrel (see Fig. 



99) droops both at night and in dull, damp weather ; it is 



erect in fine, sunny weather, droops as the seeds ripen, and 



is again erect in fruit. 



Fig. 103 shows the movements of the parts in an opening 

 inflorescence-bud of the Horse-Chestnut. 



