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it is covered assist in preventing the evaporation of its scanty 

 supply of moisture during dry periods. While rare in the North- 

 ern States, it is most abundant in the tropics, where it grows on 

 stone walls, the branches of trees, roofs of houses — in fact almost 

 anywhere it can obtain a foothoid. A great tree with all its 

 branches covered with the clustering fronds of this fern is an in- 

 teresting sight. Its ability to resist drought enables it to grow in 

 situations where it finds few competitors of any kind. 



Our common polypody, while it is not so capable of enduring 

 heat and dryness, nevertheless manages to exist under widely 

 differing conditions, as may be assumed when it is known that 

 it is found in nearly all the countries in the Northern Hemisphere. 

 In the moister atmosphere of Great Britain it is said to grow on 



walls and trees, in the mouth of wells and under hedges, and is 

 reported to wither at the approach of frost. Here it is evergreen, 

 the old fronds not only enduring a temperature of several degrees 

 below zero unharmed, but lasting for some time in the following 

 spring. 



The polypody family is one of the largest of fern families. 

 It has its best development in the tropics, where the species are 

 not only numerous but exceedjng diverse in form. The fronds 

 range from entire to very finely divided blades, aud in size from 

 those that can be covered with one's thumb to others that are two 

 or three feet across. Some produce their fronds in tufts, others 

 have slender rootstocks that ascend the trunks of trees for many 

 feet, while others have nearly the habit of climbing vines. All, 



