MAN DISPERSES SEEDS AND PLANTS. 
81 
Fig. 63. — Seed 
of cockle 
(enlarged). 
bearing plants that could be found before turning in his 
flock of sheep or the colts and cattle ; for if this were not 
done, he knows that hair and mane will surely be disfig- 
ured, and that the wool will be rendered un- 
salable. In removing the weeds he defeated 
the plans of Nature in her devices for sowing 
seeds. 
The agency of man in the distribution of 
plants exceeds in importance that of all other 
means combined. He buys and sells seeds and 
plants, and sends them to all parts of the 
habitable globe. He exterminates many plants in large 
areas, and substitutes in large measure those of his choice. 
Mixed with seeds of grasses, clovers, or grains, 
he introduces many weeds and sows them to 
grow with his crops. 
L. H. Dewey, in the Yearbook of the De- 
partment of Agriculture for the year 1896, 
p. 276, says: “Cockle seeds are normally 
somewhat smaller than wheat grains. In 
some parts of the northwest, where wheat for 
sowing has been cleaned year after year by 
steam threshers, all the cockle seeds except 
the largest ones have been removed, and these 
have been sown until a large-seeded strain 
has been bred which is very difficult to sepa- 
rate from the wheat.” For illustration, some years ago I 
purchased of a dealer in Michigan a small quantity of 
Fig. 64. — Grain 
of wheat (en- 
larged), scarce- 
ly larger than a 
seed of cockle. 
