378 



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 : 



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 .* 



Pig. 267. — Winged Fruits of Tliistle ; Winged Seeds 

 of Milkweed. 



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 iirst snow falls and 



1 See Kemer and Oliver, Vol. II, pp. 833-875 ; also Seal's Seed Dispersal. 



