38 
SEED DISPERSAL. 
strength ; some break loose after a few hard gales, while 
others are strong enough to endure many gales, and thus 
they break off a few at a time. The distance to which 
the fruit can be carried depends on the form of the 
bract, the velocity of the wind, and the smoothness of 
the surface on which the fruit falls. When torn from the 
tree the twist in the bract enables the wind to keep the 
cluster rapidly whirling around, and by whirling it is 
enabled to remain longer suspended in the air and thus 
increase the chances for a long journey. In throwing 
some of these from a third-story window, it was found 
that a bract with no fruit attached would reach the 
ground sooner than a bract that bore from two to four 
solid nuts. The empty or unloaded bracts tumble and 
slide through the air endwise, with nothing to balance 
them or steady their descent, while the fruit on other 
bracts holds them with one side to the air, which prolongs 
their descent. The less a loaded bract whirls, the faster 
its descent, and the more a bract whirls when the wind 
blows, the farther it is carried. The bract that is weighted 
with a load of fruit acts as a kite held back by a string, 
and when in this position the wind lifts the whole as well 
as carries it along. Before snow had fallen in 1896, by 
repeated moves on a well-mowed lawn, fruit and bracts 
were carried about two hundred feet, while with snow on 
the ground the distance was almost unlimited, excepting 
where there were obstructions, such as bushes and fences. 
When there is a crust on the snow and a good wind, the 
