DISTRIBUTION AND TOPOGRAPHICAL ASPECT. 



THE species of Ferns known to botanists, including the 

 lesser groups sometimes separated from what have been 

 called the ' ' true " Ferns, amount to something more than 

 three thousand. Their head-quarters are the humid forests 

 of tropical islands, in some of which they acquire a giant 

 size, and in their tree-like habit become rivals to the noble 

 Palms. The tree Ferns are not, however, numerous, the 

 number of species having this habit bearing a small pro- 

 portion to those of shrubby or herbaceous growth. 



From the statistics which have been collected in reference 

 to this question, it appears that the Ferns bear a higher 

 proportion to the flowering plants both towards the equator 

 and towards the poles ; and that their proportional number 

 is least in the middle of the temperate zone. They reach 

 their absolute maximum in the torrid zone, amid the heat, 

 moisture, and shade of the tropical forests ; and their 

 absolute minimum on the inhospitable shores of the polar 

 regions. 



