78 coville: formation of leafmold 



contrary their leaves turned purple and afterward yellowish, their 

 growth dwindled to almost nothing, and- at the end of the season 

 when compared with other blueberry plants grown in a soil mix- 

 ture in which the oak leafmold was replaced by only partially 

 decomposed oak leaves the plants in the oak leafmold were found 

 to weigh only one-fifth as much as the others. This astonish- 

 ing result is exactly contrary to the ordinary conception. We 

 have been accustomed to believe that the more thoroly decom- 

 posed the organic matter of a soil the more luxuriant its vege- 

 tation. In this case, however, thoro decomposition of the soil 

 was exceedingly injurious to the plants. 



This remarkable difference in effect between partially decom- 

 posed and thoroly decomposed oak leaves was found to be cor- 

 related with a difference in the chemical reaction of the two mater- 

 ials, the partially decomposed oak leaves being acid, when tested 

 with phenolphthalein, and the oak leafmold alkaline. 



With rose cuttings and alfalfa seedlings in the same two soils 

 exactly opposite results followed, those in the oak leafmold 

 making a luxuriant growth, those in the partially decomposed 

 oak leaves showing every sign of starvation. 



Every botanist is familiar with the rich woods where trillium, 

 spring beauty, mertensia, and bloodroot delight to grow, in a 

 black mellow mold made up chiefly of rotted leaves. He is 

 familiar too with the sandy pine and oak woods where grow 

 huckleberries, laurel, princess pine, the pink lady's slipper, and 

 trailing arbutus. The soil here also is made up chiefly of rotting 

 leaves and roots. Yet one does not look for trilliums in laurel 

 thickets, or for arbutus among the bloodroots. Either habitat 

 is utterly repugnant to the plants of the other. 



Tests of the two habitats show that the trillium soil is alkaline, 

 the other acid, reactions corresponding exactly to those observed 

 in the cultural experiments already described, rose cuttings and 

 alfalfa requiring an alkaline soil, blueberries an acid soil. The 

 difference is as conspicuous in nature as in the laboratory and 

 the greenhouse. What are the conditions under which rotting 

 leaves develop these opposite chemical reactions? 



In a ravine in the Arlington National Cemetery, near Washing- 



