166 BOTANY 
effecting cros@pollination it will be possible to mention 
only a few. 
1, In the pea family, to which the bean also belongs, 
the flower is so placed that a bee visiting it must alight 
on the wings. The weight of the bee depresses the 
' wings, which drag down the keel with them. This 
exposes the stigma and stamens. First the stigma at 
the end of the bent style strikes the insect on the under 
side of the body. Then the stamens come into contact 
with the same part. Without again touching the 
stigma, the insect flies away. Thus it does not effect 
self-pollination. On visiting another fiower, again it 
is struck first by the stigma, which receives the pollen 
brought from the first flower: thus cross-pollination is 
effected. 
2. In the primrose (Fig. 106) we have the condition 
called dimorphism (Gk. di two and morphe shape), 
1.e., there are two forms of flower. In one, known as 
the pin-eyed form, the style is long and the stigma, 
which forms at the tip a body much like a pin’s head, 
protrudes from the corolla tube. The anthers in this 
form are attached to the inside of the tube about half- 
way down. In the thrum-eyed form the positions are 
reversed: the anthers are at the mouth of the corolla 
tube, while the stigma reaches about half-way up or 
is in the same position as the anthers were in the pin- 
eyed form. A bee, pushing into a flower with short 
stamens, gets the pollen on its tongue, which it thrusts 
down for the nectar secreted at the base of the ovary. 
On now visiting a thrum-eyed flower, the insect natur- 
ally transfers to its stigma the pollen brought from the 
first flower, for here the stigma is at the same height 
as were the stamens in the pin-eyed form. In visiting 
a thrum-eyed flower the insect gets the pollen on its 
head, a position exactly suited for its transfer to the 
stigma of a pin-eyed flower. In the primrose, in cases 
where a thrum-eyed or pin-eyed flower is fertilized by 
