FLOWERS AND THEIR WOSK. 239 



The Wood Sorrel also relies largely upon small and 

 inconspicuous cleistogamic flowers for its propagation. In 

 these flowers, produced in late summer or in autumn, the 

 number of pollen-grains developed in the anthers is remark- 

 ably small (about a dozen in the smaller anthers, two dozen 

 in the larger ones), but the capsules produced are much 

 larger than those arising from the ordinary open flowers. 

 The fruits produced by the cleistogamic flowers are thrust 

 downwards into the soil, or at any rate brought close to it, 

 by the downward curvature of the flower-stalk. The fruits 

 produced by the ordinary flowers, however, show a remark- 

 able mechanism for the scattering of the seeds (Art. 291). 



265. Insects that visit Flowers. The chief flower- 

 visiting insects are beetles (Coleoptera), flies (Diptera), bees 

 and wasps (Hymenoptera), butterflies and moths (Lepidop- 

 tera). For our purposes, the chief differences between these 

 insects are the size of the body, the length of the tongue 

 (proboscis), the time of year at which each kind is most 

 plentiful, and their habits e.g. whether they collect pollen 

 or honey or both, whether they fly by day or in the evening. 



By carefully studying the structure of a flower, and noting 

 such points as the time of flowering, the order in which the 

 anthers and stigmas mature, the relative positions of anthers 

 and stigmas in the open flower and any changes in position 

 that may occur, we can often tell what kind of insect is 

 capable of effecting cross-pollination, and whether or not 

 self-pollination is possible. We shall deal later with the 

 characters of flowers which are mainly or entirely polli- 

 nated by the wind, and which lack the conspicuous colouring, 

 scent, and nectar characteristic of insect-pollinated flowers 

 (though not necessarily all present in the same flower). 



There is only one way in which to study this fascinating subject by 

 going out and patiently watching the various insects which visit flowers. 

 If you can get to know the names of the insects, do so ; in any case it 

 is usually easy to tell whether it is a butterfly or moth (four wings 

 covered with scales, proboscis often long and coiled up, feelers or 

 antennae with club-like ends in most butterflies, tapering and feathery 

 in most moths), a bee or wasp (wings membranous, body usuall}' 

 banded with yellow and black, ovipositor at hinder end of female's 

 body, used also as a sting), a fly (two clear wings with no scales or 

 hairs and few veins mostly longitudinal), or a beetle (front wings 



