SEEDS FITTED FOR WIND DISPERSAL 65 
Azores, lying 800 miles to the westward, H. B. Guppy* 
shows, from observations on the rate of fall of seeds 
made by several workers, that with a 50 miles -per 
hour horizontal wind the light-plumed seed of the 
Common Groundsel (Senecio vulgaris), for instance, 
would require to be liberated at a height of 9 miles 
above the ground if it is to reach the islands: or to 
express it differently, if liberated at ground-level, the 
seed would need to be raised 9 miles by upward eddies 
during its journey, even if corresponding downward 
eddies were absent—which they certainly never are. 
It is clear that if even light seeds are to achieve any- 
thing more than short journeys, they must depend on 
exceptional disturbances of the air, such as whirlwinds 
and tornadoes. 
It is now time to examine the devices by which 
many seeds achieve a more or less wide dispersal by 
means of the wind. Seeds possessing these adapta- 
tions may be divided into three classes: (i.) Powder 
seeds, (ii.) winged seeds, (iii.) plumed seeds. 
By powder seeds are meant seeds of very small 
dimensions. Reduction in size, if carried far enough, 
greatly facilitates dispersal by wind. This is because 
the resistance offered by the air is relatively greater 
for a smaller body than for a larger one, so that rate 
of fall decreases as the size of the falling body 
diminishes—we all know how even a heavy material, 
if reduced to powder, will fall more slowly than when 
forming a single mass. Most of the spores of the 
“Flowerless Plants ”—Ferns, Mosses, Fungi, etc_—are 
exceedingly minute, and have as a result a very slow 
* H. B. Guppy: ‘‘ Plants, Seeds, and Currents in the West 
Indies and Azores,’’ 1917, p. 425. 
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