ECOLOGY OF FLOWERS 359 
accessible to insects, but they lie open to all comers. 
They do, however, make themselves much more attractive 
and afford especial inducements in the matter of saving 
time to flower-frequenting insects by being grouped. This 
purpose is undoubtedly served by dense flower-clusters, 
especially by heads like those of the clovers and by the 
peculiar form of head found in so-called composite flowers, 
like the sunflower, the bachelor’s button, and the yarrow 
(Fig. 183). In many such clusters the flowers are special- 
ized, some carrying a showy strap- 
shaped corolla, to serve as an 
advertisement of the nectar and 
pollen contained in the inconspicu- 
ous tubular flowers (see Plate XI). 
Irregular flowers probably always 
are more or less adapted to par- 
ticular insect (or other) visitors. 
The adaptations are extremely nu- 
merous ; — here only a very few of Fic. 251.—A Beetle on the 
the simpler ones will be pointed Flower of the Twayblade. 
(Enlarged three times.) 
out. Where there is a drooping 
lower petal (or, in the case of a gamopetalous corolla, a 
lower lip), this serves as a perch upon which flying insects 
may alight and stand while they explore the flower, as the 
beetle is doing in Fig. 251. In Fig. 252 one bumblebee 
stands with his legs partially encircling the lower lip of 
the dead-nettle flower, while another perches on the sort 
of grating made by the stamens of the horse-chestnut 
flower. The honey-bee entering the violet clings to the 
beautifully bearded portion of the two lateral petals, while 
it sucks the nectar from the spur beneath. 
