coville: formation of leafmold 77 



PHYSIOLOGICAL BOTANY.— T/ie formation of leafmold.' 

 Frederick V. Coville, Department of Agriculture. 



When 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, laurel, trailing arbutus, and other plants associated with 

 them in natural distribution. 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 condi- 

 tion of alkalinity, and since the acidity of the soil is a fundamental 

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

 phenomena in the decay of leaves is essential to a correct under- 

 standing 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 com- 

 posed chiefly of partially rotted oak leaves. On the rather nat- 

 ural assumption that the more thoro the decomposition of this 

 material the more luxuriant would be the growth of the blue- 

 berry 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 disappeared. It had become a 

 black mellow vegetal mold. 



When blueberry plants were placed in inixtures containing 

 this mold they did not respond with luxuriant growth. On the 



1 Address of the retiring President, Washington Academy of Sciences, presented 

 at the annual meeting of the Academy, January 16, 1913. 



