$78 FOUNDATIONS OF BOTANY 
The student should be able, from his own observations on 
the falling fruits of some of the trees and other plants above 
mentioned, to answer such questions as the following: 
Fic. 267. — Winged Fruits of Thistle ; Winged Seeds 
of Milkweed. 
What is the use of 
the wing-like append- 
ages? of the tufts of 
hairs ? 
Which set of con- 
trivances seems to be 
the more successful of 
the two in securing 
this object ? 
What particular 
plant of the ones avail- 
able for study seems 
to have attained this 
object most perfectly ? 
What is one reason 
why many plants with 
tufted fruits, such as 
the thistle and the dan- 
delion, are extremely 
troublesome weeds? 
A few simple experi- 
ments, easily devised 
by the student, may 
help him to find an- 
swers to the questions 
above given. 
448. Tumbleweeds. — Late in the autumn, fences, par- 
ticularly on prairie farms that are not carefully tilled, often 
serve as lodging-places for immense numbers of certain 
dried-up plants known as tumbleweeds. These blow 
about over the level surface until the first snow falls and 
1 See Kerner and Oliver, Vol. II, pp. 833-875; also Beal’s Seed Dispersal. 
