174 THE NATURE AND WOEK OF PLANTS 



carry them the length or breadth of a continent, 

 across wide seas, or over mountain ranges. 



The Xanthium has an additional device not found 

 on any other known plant. This is the manner in 

 which the paired seeds germinate, one the first year 

 and the other the second. This method would enable 

 it to gain a foothold in places where it otherwise 

 might not. Thus, when the fruit is carried to a 

 field or dropped along the path of the animal to 

 which it has been attached, the coming of the 

 spring season sets one seed in action and a plant- 

 let is produced. This may survive and produce a 

 crop of fruits, in which case the species will easily 

 hold its own in this locality. On the other hand, 

 the young plant may be trampled to death by the 

 same animal which brought it to the place, it may 

 be overshadowed by other species which grow more 

 luxuriantly, or the watchful farmer may take this 

 opportunity to destroy one of the worst enemies of 

 his crops. The destruction of the first seedling 

 from any cause, however, still leaves the species 

 another chance to gain a foothold in this locality, 

 for at the beginning of the second season the other 

 seed germinates and begins the struggle for exist- 

 ence for the species all over again. 



