370 THE BIOLOGY OF FLOWERING PLANTS 



out the species it has formed the temporary habit of visiting ; 

 in this it is supplemented by the sense of form. 



These results cannot be taken to apply to insects in 

 general. It is very probable that flies, beetles, and possibly 

 butterflies and moths are more strongly affected by scents 

 than the bee. The prevalence of rather unpleasant odours 

 in fly flowers, the strong aromatic scent of butterfly flowers, 

 the stronger evening scent of those flowers pollinated by 

 night moths, tell in favour of a greater importance of the 

 sense of smell in such cases. But the hawk-moths investi- 

 gated by Knoll resembled the bee in their relation to 

 colour and scent. The proper method of attacking the 

 problem has now been worked out, and we may hope that 

 von Frisch's work will be extended to other insects, and 

 that this very interesting aspect of the relation of the flower 

 to the insect will soon be entirely cleared up. 



Special Relations. — In a very small number of cases 

 the insect visits the flower to deposit eggs in the ovary. 

 Thus Kerner states that certain Caryophyllaceae, e.g. Silene 

 nutans, S. inflata, Lychnis Flos-cuculi, are pollinated by owlet 

 moths which lay eggs in the ovary. The caterpillars devour 

 many, but not all, of the ovules and developing seeds before 

 they gnaw their way out. Small blue butterflies have a 

 similar relation to the flowers of Anthyllis Vulneraria, 

 Colutea arhorescens, and Sanguisorha officinalis. A much 

 closer relation is that between some American Yuccas, e.g. 

 Y. filamentosa, and a pollinating moth, Pronuba yuccasella. 

 The female moth first collects a little ball of pollen from the 

 anthers with special maxillary appendages ; it then lays its 

 eggs in the ovary between the ovules with the help of a long 

 ovipositor ; and finally, clambering down the style of the 

 pendent flower, it packs the pollen ball into the stigmatic 

 grooves. The plant is said to be completely sterile in the 

 absence of the moth, as when it is cultivated in Europe, and 

 the caterpillars can live only on the developing seeds, many 

 of which may be destroyed. 



Perhaps the most remarkable of all inter-relations between 

 an animal and a plant is afforded by the mode of pollination 



