MESSMATES, MUTUALISTS, AND PARASITES 



93 



Fig. 1083. Flower of Snowdrop 

 (Galanthus nivalis) 



(Galantkus nivalis, fig. 1083). Here the smooth flower-stalk is 

 bent over, so that the flower hangs down, and a creeping insect 

 trying to reach it is almost certain to fall when it reaches the 

 sharp bend. The nectar secreted in the green grooves of the 

 petals is intended for flying insects. If 

 one of these approaches from below it 

 will first touch the stigma, effecting polli- 

 nation if it has previously visited another 

 snowdrop. And in getting the nectar it 

 is sure to jolt the stamens, causing a 

 shower of pollen to fall on its back, ready 

 for transfer to other blossoms. 



A more drastic method of dealing 

 with creeping insects is found in many 

 plants which exude a sticky fluid, espe- 

 cially in the neighbourhood of the flowers, 

 or actually upon them. Sometimes this is of the nature of latex, 

 as in the Lettuce (Lactuca sativd), where the flower-heads are 

 surrounded by overlapping scales from which the milky secretion 

 readily escapes, quickly coagulating into a sticky mass that catches 

 and smothers ants and the like. The flower-stalks of Catch- Flies 

 (see p. 86) and various other forms are 

 covered by a glutinous layer, to which the 

 bodies of trespassers are often found ad- 

 hering. But more commonly the secretion 

 is poured out by variously-situated glan- 

 dular hairs. In Plumbago, for instance 

 (fig. 1084), they are borne on the calyx. 

 It would appear that in some instances the 

 captured insects are used as food, after the 

 fashion of the carnivorous plants already 

 described (see p. 68). 



So far we have dealt with the exclusion 



of wingless insects, but in the case of large flowers evolved in 

 relation to bees, wasps, butterflies, &c., small-winged insects are 

 equally undesirable visitors, since they steal nectar without 

 effecting cross-pollination. Such forms are altogether excluded, 

 or else made effective by arrangements in the flowers, which 

 Kerner thus describes in general terms (in The Natural History 

 of Plants]'. " Peculiar folds and cushions, walls and gratings, 



Fig. 1084. Flower of Plumbago 

 Europcea (enlarged), showing glan- 

 dular hairs on the calyx 



