86 coville: formation of leafmold 



the acid flora soils of this region, at an elevation of 8000 feet, 

 showed the customary high acidity at the surface, and succes- 

 sively lower degrees of acidity underneath, until at the depth of 

 5 feet, at the surface of the basaltic rock, the reaction was neutral. 



The group of plants that forms the best index to the acid char- 

 acter of a soil is the family Ericaceae, and the related families 

 Vacciniaceae and Pyrolaceae. When these occur in vigorous 

 growth on a calcareous soil or among calcareous rocks, as is some- 

 times reported, one may expect to find, as the speaker in his own 

 ^experience has always found, that a layer of upland peat has 

 been formed above the calcareous substratum and that in this 

 superficial layer the roots of the plants find their nourishment, 

 really in an acid medium, notwithstanding the alkalinity beneath. 



Continued observations on the association of certain types of 

 wild plants with acid and non-acid soils, supported by cultural 

 experiments, are in all respects confirmatory of the theory that 

 soil acidity is one of the most influential factors in plant distribu- 

 tion and plant ecology. 



The relation of leafmold to the existence of acid or non-acid 

 soil conditions may now be viewed with appreciative recognition. 

 If the conditions in any area are such that the decay of leaves 

 follows the uninterrupted course that leads to the formation of 

 leafmold a state of soil alkalinity is reached, with all the resultant 

 effects on the growth and distribution of the native vegetation. 

 If on the other hand the conditions are such that the course of 

 decay is diverted into the channel that ends in the formation 

 of peat, a condition of permanent acidity is indicated, with the 

 accompaniment of all those peculiar plant phenomena which are 

 characteristic of such a state. 



It is perhaps desirable to call attention here to the fact that while 

 partially decomposed vegetation appears to be the chief source of 

 soil acidity there are mineral constituents of the soil, of wide 

 distribution and great abundance, which are also acid in reaction. 

 The acidity of which we hear so much in agricultural writings 

 as characteristic of soils worn out by long years of careless farm- 

 ing is doubtless due in large part to a natural mineral acidity 

 unsheathed by the removal of the lime that once neutralized 



