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CHAPTERS ON EVOLUTION. 



stigma, and self-fertilisation thus becomes well-nigh an impossibility. 

 But even the form and shape or colour of a corolla or blossom may 

 be adapted either of itself, or when associated with other expedients, 

 to secure cross-fertilisation in especial conjunction with insect aid. 

 It has been pointed out that every flower of peculiar shape is 

 cross-fertilised by insects. As notable instances of this fact may be 

 cited the peas, beans, dead nettles (Fig. 230), sage (Fig. 235), salvia 

 (Fig. 232), orchids, the peculiar shape of 

 whose flowers, as well as the special arrange- 

 ments of stamens and pistil, are correlated 

 in the most exact positions to compel insects 

 to visit special parts of the flower, and thus 

 to ensure the exact performance of the work 

 of cross-fertilisation. Even the distribution 

 of colour on a flosver, and the particular 

 spots or dashes which attract our notice, are 

 guides and fingerposts directing insects to 

 the honev. Sprengel, of old, called these 

 special colour-guides macula indicantcs, and 

 Mr. Darwin remarks, that Sprengel's ideas 

 seemed to him "for a long time fanciful." 

 But the fact that these markings are most 

 commonly met with on unsymmetrical or 

 irregular flowers, the entrance into which 

 would be more likely to puzzle and con- 

 fuse insects than the apertures of symmetrical flowers, weighs in favour 

 of dashes and spots of colour being truly directive in function. 



Mr. Darwin further remarks that, in the common pelargonium, 

 the marks in question, borne on the two upper petals, are clearly 

 related to the position of the " nectary " or honey-store of the flower; 

 for when the flowers vary so as to become regular, and lose their 

 nectaries, the marks disappear. When the nectary is in part undeve- 

 loped, only one of the upper petals loses its characteristic mark. It 

 is true that humblebees are known to bite through the petals of 

 flowers, and to surreptitiously suck the honey through the apertures 

 thus made, and even hive-bees learn to utilise the holes made by 

 their larger brethren. But, notwithstanding this latter fashion ot 

 securing stolen sweets a method indicative of a certain power of 

 development in bee-intellect there can be little doubt that originally 

 to bees, as at present to insects who walk in the trodden paths 

 of their race, the colour-marks and special hues of flowers are 

 serviceable, as Mr. Darwin remarks, in guiding insect visitors 

 rapidly and without loss of time to the store of sweets, and in thus 

 enabling them to visit a larger number of flowers in a given time 

 than would otherwise be possible. Sir John Lubbock remarks, that 



FIG. 230. DEAD-NETTLE IN 

 SECTION. 



