14. 



Another condition that appears to "be responsible 

 for the presence of the epiphyte on some trees and 

 its absence from others is the character of the substratum 

 This is evident from a study of a young fern plant 

 which the writer succeeded in removing together 

 with the ba: k on v/hich it grew without injuring the 

 fern or the b^ to which it was attached, The piece 

 of bark bearing the young fern measured eight centimeters 

 in length, four centimeters in width and one centimeter 

 in thickness. The fern grew on the edge of the bark 

 pushing its young roots into the interlaminar spaces 

 so that the youngest roots branched out luxuriantly 

 about two centimeters beneath the surfe ce of the bark. 



Fig.lO 

 Upper surface of bark of 

 elm bearing the polypody 

 on its edge. 



Pig. 11 

 Lower surface of bark with 

 the polypody showing the 

 root system. 



In this manner the fern roots were really concealed 

 in the bark half way through its thickness, In this 

 position the young absorbing roots were covered by 

 a thickness of bark sufficient to serve as an excellent 

 protection against aes'iccp.tion Even when the fern 

 on the outside was apparently dried up, shriveled and 



