110 



PROTECTION OF POLLEN. 



Old World, are daily exposed to rain or heavy dew. Nevertheless their pollen 

 is never wetted, the anthers being completely shut in by the perianth-leaves, 

 which are spirally inserted on the receptacle and closely furled one upon another. 

 These flowers have a ring of stalked nectaries round the stamens, and insects 

 which visit them for the sake of the honey are obliged to break through the roof 

 formed by the overlapping perianth-leaves in order to reach the inside of the 

 flower. The pliability of these leaves enables bees by their weight to effect an 

 entrance, whilst falling drops of rain cannot penetrate, but roll off the flower. 



Pig. 221.— Protection of Pollen from Wet. 



I Ariopsis peltata. ^ Flowei of TroUius europteus. * The aame with some of the floral-leaves removed. * Digitalis lutescens. 

 s A single flower of Digitalis lutescens in longitudinal section. « Aretia glacialis. i Single flower of Aretia glacialis in 

 longitudinal section (magnified). 



Also in Corydalis, Calceolarias, Toad-Flax and Snap-dragon (Corydalis, Calceolaria, 

 Linaria, Antirrhinum) the corolla forms a closed envelope round the anthers; 

 and again in papilionaceous flowers the pollen is, up to the moment of an insect's 

 visit, hidden in the cavity formed by the two petals of the keel. 



The majority of lipped flowers — Butterwort, Yellow-rattle, Cow-wheat, and 

 Eye-bright (Pvngwicula, Rhinanthus, Melampyrum, Euphrasia, cf. fig. 220') — 

 as also the Violet (Viola), Monkshood (Aconitum,), and innumerable other plants 

 whose flowers open laterally, do not regularly inclose the pollen, but protect it 

 against rain or dew by means of an arched portion of the flower which forms 

 a roof over it. In Acanthus the flowers are inclined laterally, and, though 



