coville: formation of leafmold 79 



ton, where the autumn leaf fall from an oak grove has been 

 dumped year after year for many years, every stage in the decom- 

 position of oak leaves may be observed, from the first softening 

 of the dry brown leaf by rain to the black mellow leafmold in 

 which all traces of leaf structure have disappeared. When 

 freshly fallen the leaves show 0.4 normal acidity.- Those not 

 familiar with the chemical expression "normal acidity" may per- 

 haps most readily understand the term by reference to ordinary 

 lemon juice, which has very nearly normal acidity in the chem- 

 ical sense. Fresh oak leaves may be conceived therefore as hav- 

 ing about one-third the acidity of lemon juice, gram to cubic 

 centimeter. From a soil standpoint such a degree of acidity is 

 exceedingly high. Probably no tree or flowering plant could 

 live if its roots were imbedded in a soil as acid as this. A correct 

 appreciation of the excessive acidity of freshly fallen leaves ena- 

 bles one to understand why it is that the leaves of our lawn trees, 

 if allowed to lie and leach upon the grass, either injure or destroy 

 it. On such neglected lawns the turf grows thin, mossy, and 

 starved. 



From the height of their initial acidity it is a long descending 

 course thru the various stages of leaf decomposition to the point 

 of chemical neutrality, and then upward a lesser distance on 

 the hill of alkalinity, in the black leafmold stage. 



In order to ascertain the rate of decomposition in leaves of 

 various kinds, observations were begun in the autumn of 1909 

 on leaves of silver maple, sugar maple, red oak, and Virginia 

 pine, exposed to the weather in barrels and in concrete pits. In 

 one experiment a mass of trodden silver maple leaves 2 feet in 

 depth, with an initial acidity of 0.92 normal, was reduced in a 

 single year to a 3-inch layer of black mold containing only a few 

 fragments of leaf skeletons and giving an alkaline reaction. In 

 these experiments sugar maple leaves have shown a slower rate 

 of decomposition than those of silver maple, while red oak leaves 

 still show an acidity of 0.010 normal after three years of exposure, 



^ For a description of the method followed in determining the acidity see 

 Coville, 1910, p. 27. Experiments in blueberrj^ culture. Bulletin 193, Bureau 

 of Plant Industry, U. S. Dept. Agri. 



