334 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



When blueberry plants were placed in mixtures containing this 

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

 their leaA'es turned purple and afterward yellowish, their growth 

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

 pared with other blueberry plants grown in a soil mixture 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 astonishing result is exactly 

 contrary to the ordinary conception. We have been accustomed to 

 believe that the more thoroughly decomposed the organic matter of 

 a soil the more luxuriant its vegetation. In this case, however, 

 thorough decomposition of the soil was exceedingly injurious tojihe 

 plants. 



This remarkable difference in effect between partially decomposed 

 and thoroughly decomposed oak leaves was found to be correlated 

 with a difference in the chemical reaction of the two materials, the 

 partially decomposed oak leaves being acid, when tested with phe- 

 nolphthalein, 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, 

 sjDring beauty iClaytonia), mertensia, and blood root {Sangninaria 

 caTiadensIs) 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 {Gaylussaci-a) ^ laurel {Kdlmia lati- 

 foUa), princess pine (ChimapMla), the pink lady's slipper (Cyp- 

 ripedimn acaule), and trailing arbutus {Epigaea repens). 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 Washington, 

 where the autumn leaf fall from an oak grove has been dumped 

 year after year for many years, every stage in the decomposition of 

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



