83. 



through modifying the evaporating power of the air, it 



exerts an indirect influence on the distribution of the 



fern, 

 4, The relative humidity of the air and the air temperature 



affect the distribution of the fern only as they affect 



the evaporating power of the air, 

 5, Of all the epiphytes studied the lichens can v/ithstand 



the highest evaporation; the liverv.'ort !Frullania virp-inica 



endures the least evaporation, 

 6, The capacity of the bark for losing v/ater rapidly affects 



the fern only in its influence on the evaporation from th-« 



roots of the fern v/hich are imbedded in the bark, 

 7, The fern secures most of its necessary nitrogen from the 



humus accumulated in the crevices of the bark, The other 



mineral elements are obtained more largely from the 



dust of the air, 

 8, Where the humus of the bark shov/s a high nitrogen content, 



the fern grows luxuriantly, Where the bark is poor in 



nitrogen only a poor growth of the fern is developed, 

 9, The fern occurs equally abundantly on barks v/hich show 



an acid reaction and on those which shov/ a neutral or 



alkaline reaction, 

 10;a deeply furroT/ed,sof t bark, v:hich has a high water 



absorbing power and loses water slowly, furnishes the best 



substratum for the epiphytic fern. 



