PROTECTION OF POLLEN. Ill 



resembling bi- labiate flowers in general appearance, possess no prominent upper 

 lip, the protection of the pollen being effected by a sepal which stretches out at the 

 place where the upper lip would be. A curious arrangement for the protection 

 of pollen by sepals may be observed in the inflorescence of Hydrangea querci- 

 folia (fig. 222 8 ), a native of Florida allied to the Hortensias. The flowers of 

 this plant grow in handsome bunches, and are of two kinds: the one kind 

 includes stamens and pistil, but only a very small, greenish perianth incapable 

 of shielding the pollen of the adjoining stamens from rain or dew; the other has 

 neither stamens nor pistil, but has very large, white, expanded sepals which are 

 arranged so as to constitute with their erect stalks a sort of umbrella. The 

 flowers of the latter type are developed on the outermost and uppermost 

 branches of the inflorescence, and are always in a position to stop the rain 

 from falling upon the umbels of small pollen-bearing flowers which are situated 

 underneath them. 



In rare cases the stigmas act as pollen-protectors. The most striking instance 

 is that of the genus Iris. The stigmas in the Iris are petaloid, and consist of 

 three foliaceous structures gently curved outwards, and each terminating in a 

 pair of dentate apices (cf. fig. 220 8 ). The upper surfaces of these foliaceous 

 stigmas are convex and usually somewhat keeled along the middle line, the 

 under surfaces are concave. Beneath each stigma one finds a pollen-laden 

 anther nestling close against the concave surface, and so perfectly concealed that 

 it is impossible that it should ever be reached by a drop of water however 

 heavy the rain. 



Flowers of the form called " hypocraterif orm " by botanists are adapted to the 

 protection of their pollen on an essentially different principle. The species of Phlox 

 and Daphne included in this category, the delicate species of Primulacese belonging 

 to the genera Androsace and Aretia, which dwell amid mountain-mists, and the 

 pretty, erect-flowered Primulas (e.g. Primula farinosa, P. denticulata, P. Cash- 

 miriana), all bear flowers which are not roofed in, but have the mouths of their 

 corollas open to the sky, the tubular part of the corolla passing abruptly into an 

 expanded limb (cf. figs. 221 6 and 221 7 ), so that drops of rain or dew collect on the 

 limb surrounding the mouth of the tube. Here it seems inevitable that some 

 drops of water should reach the anthers inserted in the tube. Yet, as a matter 

 of fact, the pollen is kept dry. For, at the place where the tube passes into the 

 limb of the corolla it is abruptly contracted, besides being often also studded 

 with callosities, in consequence of which the opening is so narrowed that, 

 although insects with fine probosces gain access to suck the honey in the 

 flower, any rain-drops that may happen to be lying upon the limb do not gain 

 admission because the air cannot escape from the tube. If flowers of Aretia 

 glacialis (fig. 221 6 ), a plant growing on the moraines of glaciers, are examined 

 after a shower, it is found that every one has a drop resting upon it which 

 slightly compresses the air in the narrow tube of the corolla, but cannot reach 

 the pollen upon the anthers lower down the tube. A subsequent shake or puff 



