THE SEED 



23 



the four agencies named, animals and wind are the most effec- 

 tive, and the greater number of adaptations observed will be 

 found to have reference to these. 



20. Involuntary dispersal. - - The lower animals may be 

 voluntary agents in a way, though not designedly so, as when 



FIG. 37. Good quality of clo- 

 ver seed. 



FIG. 38. Inferior quality of 

 clover seed mixed with " screen- 

 ings." 



a squirrel buries nuts for his own use and then forgets the lo- 



cation of his hoard and leaves them to germinate ; or when 



a jaybird flies off with a pecan in his bill, intending to crack 



and eat it, but accidentally lets 



it fall where it will sprout and 



take root. Both man and the 



lower animals are not only in- 



voluntary, but often unwilling 



agents of dispersal. Some of the 



most troublesome weeds of civili- 



zation have been unwittingly dis- 



tributed by man as he journeyed 



from place to place, carrying, 



along with the seed for planting 



his crops, the various weed seeds, 



nr "ciprpprnncrc: " Q thp^p rmvtnrp^ 



enmgs, as tnese mixtures 

 are called by dealers, with which 

 they have been adulterated either through carelessness and 

 ignorance, or from unavoidable causes. The neglected 

 animals, also, that are allowed by short-sighted farmers to 

 wander about with their hair full of cockleburs and other 



FlG ' 39. Dodder on red clover, 



showing how the seeds get mixecL 



