REPRODUCTIVE ORGAJSS 



117 



Fig. 120. A common tumbleweed ( C^cto/oma). 



of pine and catalpa. Plumes and tufts of hairs are devel- 

 oped by the seed-like fruits of dandelion, thistle, and very 

 many of their relatives, and by the seeds of the milkweed 

 (see Figs. Ill, 112, 113, 111). On plains, or level stretches, 

 where winds are 

 strong, a curious 

 habit of seed dis- 

 persal has been de- 

 veloped by certain 

 plantsknown as 

 '' tumbleweeds " or 

 ^^field rollers. '^ 

 These jilants are 

 profusely branching 

 annuals with a small 



. Fig. V2l. The 3-valved fruit of violet discharging 



root system in a its seeds—After Beal. 



