222 RECEPTION OF FLOWER-SEEKING ANIMALS AT THE FLOWER. 



important of all, with advantage to the plant itself. It were a contradiction for the 

 invited guests on their arrival to find the honey-secreting flower inaccessible, or 

 that a flower should remain widely open when no more nourishment was to be 

 obtained when the meal, so to speak, was finished. 



These obvious truisms apply to flowers still in bud, which it would be premature 

 for insects to visit, and to such as have no further need of insects. It commonly 

 happens that when a flower is pollinated its means of attraction coloured or 

 scented corolla disarticulates and falls off. But cases exist in which the petals, 

 having served this purpose, do not at once fall away, but are retained, having 

 another part to play. When this is the case it is undesirable that they should 

 interfere with the other younger flowers by competing with them for visitors; in a 

 word, they must be rendered inaccessible. This is most frequently accomplished by 

 the petals assuming the position they occupied in the bud, and often enough such a 

 flower absolutely resembles a bud, as in the Yucca, represented in fig. 240 l , p. 157. 

 Sometimes a lobe of the perianth or of the sheath-like spathe folds down, 

 obstructing the entrance, as in many Aroids, and, in particular, in the Birthwort 

 (Aristolochia Clematitis, cf. fig. 257 8 ). In a number of cases the old flowers, 

 which have no further need of insects, bend down out of the way of the younger 

 ones, as may be seen in a number of Papilionacese and Boraginese (cf. vol. i. p. 744). 

 In Morina Persica and in the Brazilian Rubiacea, Exostemma longiflorum, the old 

 flowers not only bend down, but undergo a peculiar change in colour, so that they 

 are no longer noticed by insects. At the time of flowering the tubular corollas of 

 these flowers are white and attractive to night-flying moths, being visible in the 

 dark at some distance; but as soon as they are pollinated the corollas fade and 

 bend down, assuming ere the following night a lurid red tinge, so that they are 

 no longer visible in the dark. 



It is similarly capable of easy demonstration that flowers provided with allure- 

 ments for animals become conspicuous and accessible only at that period when visits 

 are of real advantage. Their accessibility is then promoted as much as possible. In 

 addition to being open the flowers are directed towards the side from which the visits 

 of the most welcome guests are expected. In many plants, of which the Crown 

 Imperial (Fritillaria), Foxglove (Digitalis), and Campanula may serve as types, 

 the at first erect flower-stalks bend down sharply just before the opening of the 

 flowers, so that the entrance is directed towards the ground. This position is 

 inconvenient and unsuited to animals which would suck the honey, hovering over 

 the flowers, to flies, accustomed to lick up honey from a flat surface, to such insects 

 as are too timid to venture into the inside of a hollow flower, finally to beetles 

 which require large amounts of deposited pollen. To bees and humble-bees, how- 

 ever, these flowers are accessible; supported by the projecting stigmas, style, and 

 stamens, or sometimes by hairs, they easily climb up to the honey-secreting dome 

 of the bell. Probably these insects prefer bell-shaped flowers, since here they have 

 no competitors to fear. The ready welcome thus offered to the most industrious of 

 all flower-visitants has this further advantage, that the desired transfer of pollen 



