INTELLIGENCE OF THE CELL 



255 



obstruction, such as a fence, great masses of these tumble- 

 weeds may be seen lodged against the windward side. 

 This method of dispersal is far more effective than the 

 mechanical discharge ; but it is fitful, and its range usu- 

 ally is not very great. Thistle-down may be floated into 

 a neighboring field, and a strong wind may carry the 

 comparatively heavy-winged fruits of the maple and the 

 elm some distance ; but at best the scattering is only over 



FIG. 35. Seeds of beggar-ticks with barbed appendages. 



a neighborhood. In many cases seeds or fruits or heads 

 develop grappling appendages of various kinds, forming 

 the various burs, which lay hold of animals brushing 

 past; and so the seeds are dispersed." 



The skillful performance of the Russian thistle and the 

 tumbleweed is wonderful, while they are growing during 

 the summer. You can not possibly pull a plant out by 

 the roots, but as soon as it is ripe for seed dispersal, it 

 is cut loose by the cells that made it, and stands ready 



