80 coville: formation of leafmold 



and leaves of Virginia pine an acidity of 0.055 normal under the 

 same conditions. 



The alkalinity of leafmold is due chiefly to the lime it contains, 

 the lime content expressed in terms of calcium oxid often reach- 

 ing 2 to 3 per cent of the dry weight. One sample had a lime 

 content of 3.55 per cent. Many of the soils that result directly 

 and exclusively from the decomposition of limestone have a 

 lower percentage of lime than this. An alkaline leafmold con- 

 taining 2 to 3 per cent of lime is properly regarded as a highly 

 calcareous soil. Yet such a deposit may be formed in a region 

 where the underlying soil is distinctly noncalcareous, the lime 

 content of the soil being only a small fraction of 1 per cent and 

 the soil reaction being acid. Whence comes the abundance of 

 lime in an alkaline, richly calcareous leafmold formed over a soil 

 distinguished by an actual poverty of calcareous matter? 



If the leafmold is rich in lime the leaves from which it is de- 

 rived should also be rich in lime. A determination of the amount 

 of calcium oxid in the dried freshly fallen leaves of some of our 

 well known trees shows this to be true, as illustrated by the fol- 

 lowing selections: 



Per cent of 

 Kind of leaves calcium oxid 



Red oak {Quercus rubra) 1 . 73 



Silver maple {Acer saccharinum) 1 . 88 



Pin oak {Quercus palustris) 1 . 91 



Sweet gum {Liquidamhar styraciflua) 1 .92 



Bur oak {Quercus macrocarpa) 2 . 39 



Sugar maple {Acer saccharum) 2.56 



Tulip tree {Liriodendron tulipifera) 2 . 84 



Hickory {Hicoria myristicaeformis) 3 . 66 



Gingko {Ginkgo biloba) 4 . 38 



It should be understood that the lime thus shown does not 

 exist in the leaf in the form of actual calcium oxid. It is largely 

 combined with the acids of the leaf and serves in part to neutralize 

 them, but is insufficient in amount to effect a complete neutral- 

 ization. In all the kinds of leaves and herbage thus far examined, 

 the net result is an acid condition altho lime may be present in 

 large amount. Thus in the leaves of silver maple a condition 

 of excessive acidity exists, about 0.9 normal, notwithstanding 

 the presence of nearly 2 per cent of lime. 



