VII. THE WAY IN WHICH NEW PLANTS 



ARISE 



178. Distribution of the individuals of a species. 

 Every species is represented by a number of 

 individuals. Sometimes this number is very great 

 and may run up into the millions. On the other 

 hand, there are a number of species of which but 

 few individuals have been seen, and some are so 

 rare that but a single specimen may have been 

 found. The individuals of a species may be scat- 

 tered across states and continents, or they may be 

 congregated in a meadow or on a single mountain 

 top. Thus, for instance, the common polypody 

 forms carpets or dense layers on rocks, that contain 

 several dozens of individuals, and these colonies may 

 be found almost throughout North America, Asia, 

 and Europe. The individuals of Adam-and-Eve, or 

 putty root, occur one or a few in a place, in a 

 broad belt of country that includes the northern 

 half of the United States and the southern half 

 of Canada. The Georgia oak (Quercus Georgiana) 



130 



