REPRODUCTION BY SEED 171 
so much honey in the tube that it is sometimes half-full, 
when it can just be reached, though with difficulty, by 
the humble-bee. The only effective visitor to the large- 
flowered climbing convolvulus—Convolvulus sepium—is 
the hawk-moth. In many highly specialized flowers 
heavy structures have to be pushed aside before the 
honey can be obtained—e.g., snapdragon, calceolaria, 
gorse, broom. Mock glands occur in some flowers—e.g., 
grass of Parnassus. Sham nectaries, in the form of little 
green knobs, are found at the base of the corolla-lobes 
in the woody nightshade. 
Some flowers have very 
few visitors. This is either 
because they are so 
specialized that very few 
insects can get at the 
honey, or because they 
are disagreeable to all but 
one or two insects. In 
extreme cases, flowers, 
though seemingly well 
adapted to insects, seldom 
get a visitor, and have to 
rely upon their own pollen. 
The violet is a case in 
point. By scent, form, 
and honey it seems a 
plant flaunting everything 
that could attract insects ; 
but few come, and seeds 
as usual] y formed by self- a, honey-leaf ; 6, carpels ; c, stamens ; 
fertilization in closed buds. d, sepals ; e, receptacle. 
Other flowers seem to be 
adapted to one insect, and no other. They are probably 
disagreeable to other insects. For example, Lysimachia 
vulgaris, the yellow loosestrife, is only visited by one 
insect—a bee (Macropis labiata); Trifolium repens, the 
white clover, relies on the humble-bee ; and the white 
bryony (Bryonia dioica) is pollinated exclusively by the 
bee Andrena florea. 
Since the position of the nectaries determines so 
largely the kind of insects visiting the flowers for 
food, we may roughly divide entomophilous flowers 
Fic. 71. — Monx’s- Hoop: Lonaer- 
TUDINAL SECTION OF FLOWER. 
