48. 



making the chemical analyses. The results of these 

 analyses aire presented in Talale IV, 



A study of the data reveals the fact that wijere 

 nitrogen was abiindant, the clumps of the epiphytic fern 

 were fairly large, That the nitrogen was not obtained from 

 the dust of the air is evident from the fact that samples 

 which showed a high percentage of silicon, generally 

 showed a low percentage of nitrogen; where the. silicon 

 content was low the nitrogen content of the sample was 

 high, Regarding the silicon content as an index of the 

 amount of dust accumulated in the crevices of the bark 

 (since silicon is abundant in the dust of the region), 

 it appears that the main source of nitrogen was not 

 the dust of the air but the accumulated decaying 

 organic matter which composed the bulk of the humus 

 and which eradiated on the bark through the masses, 

 of epiphytic bryophytes and animal matter associated 

 with them,The luxuriant growth of therern on the 

 substratum rich in giitrogen indicates that the nitrogen 

 content of the substratum has a marked effect on the 

 development and grov/th of the polypody ,This is particularly 

 evident in ta case of Crataegus which, in spite of 

 possessing a smooth bark and being only slightly over 

 eight centimeters in diameter, vas able to support a good 

 sized clump of the polypody, doubtless due to the high 

 nitrogen content of the humus on which it thrived. 



