22 THE STORY OF PLANT LIFE 
flower, and if there is a long and short style, as in 
the Primrose, it is dimorphic; if there is an inter- 
mediate type also it is trimorphic, as in Purple 
Loosestrife. This requires the transfer for effective 
pollination of pollen from a long-styled form to a 
long-stamened form, and so on. By this means 
the possibility of self-pollination is minimised. 
This is called legitimate pollination; whilst if a 
long-stamened and short-styled form are crossed 
the pollination is illegitimate. 
There are other methods by which the pollination 
of the flower is rendered effective, described under 
each species, such as piston movement in Ulex, etc.; 
loose-pollen forms where the pollen is dry and ina 
box arrangement, as in Eyebright; porous anthers, 
as in Heath; trap-flowers,asin Arum; cleistogamic 
flowers, as in the Violet ; honey guides or spots on 
flowers to guide to the honey. Some foreign plants 
are pollinated by animals, such as snails, bats, 
humming birds. 
Most water plants are pollinated by insects or the 
wind. But a few, such as Elodea and Vallisneria, 
do so by pollination at the surface by aid of water, 
whilst in Ruppia and Grass-wrack this is accom- 
plished below the water. 
PLANTS AND SEED DISPERSAL. 
When the flower has been pollinated it is fertilised | 
by the passage of pollen grains down the stigma and 
