34 
SEED DISPERSAL. 
Low hop clover, an annual with yellow flowers, which 
has been naturalized from Europe, has developed recently 
on strong clay land into a tumbleweed six inches in 
diameter. The tops of old witch grass, Panicum capillare, 
and hair grass, Agrostis hy emails, become very brittle when 
ripe, and snap from the 
parent stem and tumble 
about singly or in masses, 
scattering seeds by the 
millions. I have seen 
piles of these thin tops 
larger than a load of hay 
where they had blown 
against a grove of trees, 
and in some cases many 
were caught in the tops 
of low trees. 
Bug seed and buffalo 
bur are tumbleweeds. 
In autumn the careful 
observer with an eye to 
this subject will be 
rewarded by finding 
many other plants that 
behave more or less as tumbleweeds. Especially is this the 
case on prairies. These are annuals, and perish at the close 
of the growing season. There are numerous other devices 
by which seeds and fruit secure transportation by the wind. 
Fig. 26. — The top of old witch grass as a tumble- 
weed. (Reduced two thirds.) 
