166 BRITISH PLANTS 
at any time. During the summer they bloom freely, but 
few fruits are formed. In late summer and early autumn, 
when cold, damp weather is frequent, flower-buds form 
which never open, and these always produce a full com- 
plement of seed. 
Cross - Pollination.—The pollen may come from a 
different flower on the same plant (geitonogamy, Gr. geiton, 
neighbour) or from another plant. Geitonogamy is not far 
removed from self-pollination, for the sexual elements are 
both derived from the same plant, though the relationship 
is not so close as between the stamens and pistil of the 
same flower. In true cross-pollination two distinct plants 
must co-operate, one contributing the pollen, and the 
other the ovules. 
Agents of Pollination.—In self-pollinated flowers the 
pollen either falls by its own weight upon the stigma or 
the two are brought into contact by the bending of the 
stamens or styles. In cross-pollinated flowers an external 
agent is required to carry the pollen from one flower to 
another. 
1. Water.—Water carries the pollen only in the case of 
a few water-plants where the flowers are completely sub- 
merged all the time. Most flowering aquatics send up 
their flowering shoots above water, and these are pollinated 
in the same way as land-plants. The floral habits of a 
plant are more conservative than its vegetative organs, 
and the persistence of the aerial mode of pollination in 
aquatics affords strong evidence of their terrestrial origin. 
The grass-wrack (Zostera) found on muddy shores is an 
example of water-pollinated flowers. It flowers below 
water. The pollen is long and thread-like, and of the 
same density as sea-water. It is borne passively to the 
stigmas by the movements of the water, just as in wind- 
pollinated plants the pollen is carried passively through 
the air by the wind. 
2. Wind.—In wind-pollinated flowers the pollen is 
light and powdery. It is produced in enormous quantity, 
for the wind bloweth where it listeth, and the chance of 
the pollen reaching its proper destination—i.e. the 
stigmas of a flower of the same species—is very small. 
Anemophilous flowers (Gr. anemos, wind ; phileo, I love) 
have no need for attractive and sweet-scented corollas. 
Not being visited by insects, they secrete no honey. The 
