49. 



Although the ash of the epiphyte, as a rule, shows 

 a high percentage of potash, the "humus" genera, lly 

 shows a low potash content^which seems to indicate 

 that most of the potash obtained by the plaint comes 

 from the dust of the air. This is probably true also 

 for the phosphoric acid, for very small sunounts of this 

 substance were found in the "humus", while the ash of 

 the epiphyte shov/ed a much higher percentage of the 

 acid, It is possible that the high phosphoric acid 

 content in the ash of the epiphyte is due to metabolic 

 processes.lt is evident from the chemical study that 

 the fertility of the substratum is of as much importance 

 to development and growth of the fern as are the low 

 rate of evaporation and an abundance of moisture for 

 the beginning of the epiphyte on the tree, It is indeed 

 remarkable that the nitrogen of the humus on the bark 

 of the tree is frequently as high and at times even 

 higher than the nitrogen content of the most fertile 

 so]]iyS,for very few soils have as much as 1,6% nitrogen. 

 It is no v/onder, then, that the polypody thrives so well 

 on such trees as Q.uercus stellata. Juniperus virginiana . 

 or Ulmus emer i cana and developsion these trees an extensive 

 root system euad an abundance of leaves. 



Acidity and Alkalinity Tests of the Substratum. 

 Chemical determinations in the field, by means of 

 the La Motte set of indicators, cf the acidity of the bark 

 of trees on v/hich the epiphytes occurred and also of the 



