THE FORMATION OF LEAFMOLD. 



By Frederick V. Coville. 



Wlien the leaves of a tree fall to the ground they begin to decay 

 and ultimately they are disintegrated and their substance becomes 

 incorporated with the other elements of the soil. The same thing 

 happens with the leaves, stems, and roots of herbaceous plants. 

 Such organic matter is one of the chief sources of food for plants, 

 and its presence in the soil is therefore of fundamental importance 

 in the maintenance of the vegetative mantle of the earth. 



In a series of experiments from 1906 to 1910 the speaker showed 

 that a condition of acidity is a primary requirement of the blue- 

 berry {Vaccinimn), laurel (K almia latifoUa) ^trnilmg a.Ybnti\s {Epi- 

 gaea repent), and other plants associated with them in natural dis- 

 tribution. Other kinds of plants and plant associations require, on 

 the contrary, a neutral or alkaline soil. 



It is the purpose of the present address to show how the leaves of 

 trees in the process of the formation of leafmold produce at one 

 time or under one set of circumstances a condition of soil acidity, at 

 another time or under other circumstances a condition of alkalinity, 

 and after calling attention to the acidity of the soil as a funda- 

 mental factor in plant ecology, to point out that a knowledge of 

 certain phenomena in the decay of leaves is essential to a correct 

 understanding of the distribution of vegetation over the surface of 

 the earth and its adaptation to the uses of man. 



In the early experiments with blueberries it had been found that 

 these plants grew successfully in certain acid soils composed chiefly 

 of partially rotted oak leaves. On the rather natural assumption 

 that the more thorough the decomposition of this material the more 

 luxuriant would be the growth of the blueberry plants, some old oak 

 leafmold was secured for further experiments. It had been rotting 

 for about five years and all evidences of leaf structure had disap- 

 peared. It had become a black mellow vegetal mold. 



1 Address of the retiring president, Washington Academy of Sciences, presented at the 

 annual meeting of the Academy, Jan. 16, 1913. Reprinted with author's revision from 

 the Journal of the Washington Academy of Sciences, vol. 3, pp. 77 to 89, Feb. 4, 1913. 



333 



