42 
SEED DISPERSAL. 
Fig. 31. 
are ready for a flight, and it does n’t take much to carry 
them for a long distance. As an active boy delights to 
venture again and again over thin ice on a shallow pond 
in the pasture, half fearing, yet half hoping, that he may 
become a hero by breaking through and escaping, so like- 
wise many of these seeds and 
seed-like fruits spread them- 
selves out, as if to tempt the 
wind to come along and attack 
them. 
The twin fruits of the pars- 
nip and some of its near 
relatives are light and thin 
and split apart, each holding 
on lightly to the top of a 
slender stem. In this position 
they are sure to be tom off sooner or later. Somewhat 
after the manner of the willow-herb behave the pods and 
seeds of willow r s, poplars, milkweeds, Indian hemp, and 
cotton. 
24. Why are some seeds so small? — Do you know why 
so many kinds of plants produce very small and light 
seeds ? W ould it not be better if they produced fewer 
and larger seeds, which would then be stronger and better 
able to grow under adverse conditions ? But a large 
number of small seeds cost the plant no more effort than 
a small number of large ones, and the lighter and smaller 
the seeds and the more there are of them, the better their 
Dry twin fruits of the parsnip 
held by slender stems ready to be 
blown away. (Much enlarged.) 
