108 PROTECTION OF POLLEN. 



higher temperature than would otherwise have been the case. This explanation 

 must be borne in mind. 



We find, therefore, an amount of variety in the forms of safeguard against 

 wet corresponding to the multiplicity of the adaptations which subserve the 

 purpose of pollen-transport by the wind or by butterflies, bees, beetles, or flies, 

 as the case may be. The means of protection are diversified also according to 

 whether the cover is placed immediately over the pollen or over an entire group 

 of flowers, whether it shelters the newly-opened, pollen-laden anthers or that part 

 of the flower whereon pollen liberated from the anthers is temporarily deposited; 

 and again they vary according as it is the anther- walls, stigmas, petals, involucre, 

 or foliage-leaves which have to serve as roof to the pollen. The Lime-tree affords 

 an instance of the last-mentioned arrangement, its flowers being invariably so 

 placed that at the time when pollen is yielded by the anthers they are covered 

 by the broad, flat foliage-leaves. However sharp the showers to which a Lime-tree 

 is subjected the rain-drops roll off" the blades of the leaves, and it is only by 

 exception that any one of the many flowers stationed beneath them is wetted. 

 The same provision is met with in a few species of Daphne (e.g. D. Laureola and 

 D. Philippi), in several Malvaceae (e.g. Älthcea pallida and Ä. rosea), and in the 

 Tinpatiens Nolitangere, a plant which possesses other remarkable features and 

 will be the subject of further discussion by and by (c/. fig. 220 ^). In Impatiens 

 the flower-buds are held by their delicate stalks above the surfaces of the leaves 

 from whose axils they spring, and the leaves are at first folded upwards like 

 erect troughs. Subsequently, when the buds get bigger and their stalks longer, 

 the latter slip down to one side of the leaves and hide beneath them, whilst the 

 leaf-margins still continue to be curved upward. The leaf then flattens itself out 

 and fixes the drooping flower-stalk by means of one of the lobes of its heart-shaped 

 base, and thus indirectly keeps the suspended bud in position, so that when later 

 on the bud and its anthers open, which they do simultaneously, they are roofed 

 over by a smooth lamina, off" which the rain-drops roll \vitliout ever wetting the 

 flowers or their pollen (fig. 220 ^). 



In many Aroidese the spadix is completely covered by the large sheathing 

 leaf or spathe at the time when the anthers burst, as, for instance, in the curious 

 Japanese Arisema ringens, where the spathe curves over the inflorescence like 

 a Phrygian cap, and in Ariopsis p)eltata, where the spadix is protected from rain 

 and dew by a sheathing leaf resembling a boat with the keel uppermost (c/. 

 fig. 221^). Genetyllis tulipifera, a shrub belonging to the Myrtacese, bears at 

 the ends of slender, woody twigs inflorescences which at first sight might be 

 taken to be pendent tulips. On closer inspection it appears that the large white 

 leaves with red veins which recall the leaves of the tulip perianth are involucral 

 bracts which cover the closely-crowded flowers and shield them from the rain. 

 Similarly in the case of the Banana and its allies {Mvusa, Ravenala) the flowers 

 are covered over when the pollen is mature by large involucral sheaths which 

 subsequently, after the pollen has been used up and there is no longer any need 



