ARRANGEMENTS TO PROMOTE CROSSING. 



307 



turn. The stigmas in the centre of the flower are still folded together: as soon as 

 they begin to separate the anthers fall away from their filaments, and the five 

 mature outspread stigmas are surrounded only by the needle-shaped filaments 

 minus their anthers (fig. 291 ^, the left-hand flower). The same thing happens in 

 some Saxifrages, of which Saxifraga rotundifolia (fig. 292) will serve as a type. 

 After the petals have unfolded, a peculiar action on the part of the stamens is to be 

 observed for several days. Each anther as it dehisces is raised up by its filament 

 into an erect position (see fig. 292 ^), but remains in this position only for a short 

 time; it bends down again the next day or the next but one, resuming its original 

 position. The anther falls ofi", or if it remains as a shrivelled mass on the top of 

 the filament it has by this time lost all its pollen. All the stamens in succession 



291.— Completely dichogamous Plowers. 



1 Geranium sylvaticum with completely protandrous flowers. 2 Parietaria officinalis with completely protogynous flowers. 

 3 Single flowers of Parietaria with mature brush-shaped stigma and closed coiled-up stamens. * The same flower at a 

 later stage of development ; the stigma has fallen off, the fllaments have straightened, and the anthers are flirting out 

 ' their dusty pollen. 1 and 2 nat. size; 3 and * somewliat magnified. 



undergo this rising and sinking. Not until all the pollen has disappeared do the 

 two short styles, which up till now have been folded together like the two ends 

 of a pair of tongs (fig. 292^), separate from one another, and their stigmas become 

 capable of pollination (fig. 292'^). The Grass of Parnassus {Parnassia 'palustris; 

 see fig. 267*, p. 249) as well as many Caryophyllacese (e.g. Alsine verna, Silene 

 Saxifraga), many Valerians (e.g. Valerius J. officinalis) and Tulips (e.g. Tulipa 

 Didieri) exhibit the same course of development, especially the falling away of 

 the anthers. In Caryophyllacese it often happens that the antherless filaments bend 

 down in a semicircle under the petals and become so hidden that the flower might 

 at first sight be thought to be pistillate instead of truly hermaphrodite. 



The end gained by this shedding of the anthers in the Balsam, Saxifrage, Grass 

 of Parnassus, Chickweed, Pink, and numerous other plants with hermaphrodite 

 flowers, is also obtained in the following manner: — The anthers are covered over 



