140 NATURAL FERTILISATION 



purplish anthers hanging at the ends of filaments of extra- 

 ordinary delicacy, or rather of empty anther-sacs from which 

 every grain of pollen has been discharged. These anthers 

 appear, when they have arrived at maturity, to break suddenly 

 out of the opening bud, the filament elongating in a moment 

 to several times its original length, the anther bursting at the 

 same time, when the slightness of its attachment to the filament 

 causes the least breath of wind to sweep the whole of the light 

 dusty pollen out of its case, some of which must necessarily 

 reach the neighbouring stigmas in the same ear, provided there 

 is not enough wind to blow it completely away. In Rye and 

 Oats this extraordinarily rapid lengthening of the filaments is 

 even more conspicuous than in Wheat. Hence the importance 

 attached by farmers to comparatively calm sunny weather at 

 the critical period when the corn is in flower. These two ex- 

 amples furnish good illustrations of the structure which prevails 

 in those flowers that are fertilised by the wind. They are 

 generally of very simple structure, and rarely brightly coloured, 

 since bright colours would be of no advantage to them. The 

 quantity of pollen is usually very large, and the structure of the- 

 male flowers such that it is dispersed by the wind with the 

 greatest facility, this being brought about by the slender 

 " versatile " filaments of the Wheat and by the lightly hanging 

 catkins of the Hazel, the Willow, and other early-flowering 

 shrubs, which appear before the leaves, and hence at a period 

 when there is no obstruction to the free dissemination of the 

 pollen. In the majority of flowers, however, the structure of 

 the pollen, or the arrangement relatively to one another of the 

 pistil and stamens, is such that fertilisation could not be 

 effected by the wind alone. Sometimes the pollen-grains 

 themselves are too large and heavy to be thus conveyed, or 

 they are united together by fine threads or even into dense 

 masses ; or the position of the stigmatic portion of the pistil is 

 evidently not adapted for the pollen to reach it in this way ; 

 and Nature then employs as the agent in fertilisation the 

 services of insects or of other small animals. This opportunity 

 is afforded by the visits of insects to the flowers in search of 

 the honey or nectar which forms an important portion of the 

 food of many classes. 



Agency of Insects. 



The attraction to the flowers which serve insects foi^food is 

 twofold scent and colour; in other words, those properties 

 which chiefly render flowers attractive to our own senses. The 



