234 FLOWEKS AND THEIR WORK. 



conspicuous inflorescences; they usually secrete honey and 

 give out perfume. Pollen is not usually produced in great 

 abundance, as the provision for its transference is more 

 perfect. The bright corollas, the perfume and honey, serve 

 to attract insects. In return for the service rendered by 

 insects the flowers sacrifice part of their nutritive substance 

 in providing food to the insects (honey and pollen), and make 

 a further sacrifice of material in developing a coloured 

 perianth which will attract the insects. 



A honeyless but otherwise insect-attracting flower is 

 sometimes called a "pollen-flower," examples being seen in 

 Poppies, Dog Eose, Rock-rose (not a true Eose), Wood 

 Anemone, Traveller's Joy, St. John's Wort, Gorse, Broom, 

 Meadow-sweet. 



In many cases the corolla is so modified that the insect 

 must alight on the flower or enter it in a special way (e.g. 

 Labiates, Papilionaceae) ; the same result may be attained by 

 the secretion of nectar into special receptacles or spurs (e.g. 

 Violet) ; or the insect, on entering a flower, pushes against 

 special processes or outgrowths which move the stamens and 

 bring the anthers in contact with its body (Sage), etc. 



The general result of all these devices is that the insect re- 

 ceives the pollen on a special part of its body, and when it 

 enters another flower the pollen is deposited on the stigma. 

 In many protandrous flowers this is secured by the style 

 bending over so that the stigma is in the position formerly 

 occupied by the stamens. 



The condition known as heterostyly is seen in the Primrose, 

 which has two types of flower borne on different plants. One 

 kind has long stamens (with anthers in the throat of the 

 corolla tube) and a short style ; the other has a long style 

 and short stamens ; thus in the two types the positions of 

 anthers and stigma are simply reversed. Evidently pollin- 

 ation will be most readily effected by transference between 

 these two forms, and not between two flowers of the same 

 form ; and experiment has proved that the best seed is 

 produced when this is the case. 



In the Primrose there are two kinds of flower; this is 

 the dimorphic type of heterostyly. In Purple Loosestrife 

 (Lythrum) there are three with long, short, and medium 

 styles; this is the trimorphic type. Heterostyled flowers 



