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216 A TEXTBOOK OF GENERAL BOTANY 
wind-pollinated species produce their flowers above the foliage, 
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Fie. 217. Pollination of Vallisneria gigantea; 
size of flowers exaggerated 
Left, a female plant with a flower floating on the 
surface of the water ; right, a male plant with two 
spikes of male flowers. The covering of the spike 
at the left is open and the flowers are becoming 
detached and rising to the surface, where they open 
and float. The stamens of one male flower are in 
contact with the stigma of the female flower 
have leaves, as is 
the case with many 
trees of the temperate 
zone which produce 
their flowers early in 
the spring before the 
leaves have appeared. 
Either ¥ef these “are 
rangements increases 
the chance of pollen’s 
reaching the stigma. 
W ind-pollination is 
especially adapted to 
species which grow 
together in large num- 
bers, rather than to 
those which are scat- 
tered in mixed stands. 
Since grasses often 
cover quite extensive 
areas, they are very 
well adapted to this 
method of pollina- 
tion, as are also for- 
est trees which grow 
in stands of one or a 
few species. Wind- 
pollination is much 
more frequent in the 
forests of the temper- 
ate zone, which are 
composed of one or 
a few species, than in the forests of the moist tropics, where 
the stand as a rule is made up of a great variety of trees. 

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