FORMATION OF LEAFMOLD COVILLE. 337 



due in large part to the lime accumulated on the forest floor by the 

 trees in preceding centuries, and to the consequent alkalinity of such 

 surface soils when the timber had been removed and the leaf litter 

 was thoroughly decomposed. After a generation or two of reckless 

 removal of crops the surface accumulation of lime was depleted and 

 unless the underlying soil was naturally calcareous a condition of 

 infertility ensued, which, for the purposes of ordinary agriculture, 

 could be remedied only by the artificial application of lime. 



The chief agents in the decay of leaves are undoubtedly fungi and 

 bacteria. There are other agencies, however, that contribute gTeatly 

 to the rapidity of decay. Important among these are earthworms, 

 larvtB of flies and beetles, and myriapods or thousand-legged w^orms. 

 Animals of all these groups exist in myriads in the leaf litter. They 

 eat the leaves, grind them, partially decompose them in the process 

 of digestion, and restore them again to the soil, well prepared for the 

 further decomposing action of the microscopic organisms of decay. 



The importance of earthworms in hastening the decay of vegetal 

 matter was pointed out long ago by Darwin in his classical studies 

 on that subject. The importance of myriapods, however, as con- 

 tributing to the formation of leafmold has not been adequately 

 recognized. In the canyon of the Potomac Eiver, above Washington, 

 on the steeper forested talus slopes, especially those facing north- 

 ward, the formation of alkaline leafmold is in active progress. The 

 purer deposits are found in pockets among the rocks, where the leaf- 

 mold is not in contact with the mineral soil and does not become 

 mixed with it. The slope directly opposite Plnmmers Island is a 

 good example of such localities. Here during all the warm months 

 the fallen leaves of the mixed hardwood forest are occupied by an 

 army of myriapods, the largest and most abundant being a species 

 known as Spiroholus inarginatus. The adults are about 3 inches in 

 length and a quarter of an inch in diameter. They remain under- 

 neath the leaves in the daytime and emerge in great numbers at 

 night. On one occasion a thousand were picked up by Mr. H. S. 

 Barber on an area 10 by 100 feet, without disturbing the leaves. 

 On another occasion an area 4 by 20 feet yielded 320' of these myria- 

 pods, the leaf litter in this case being carefully searched. Every- 

 where are evidences of the activity of these animals in the deposits 

 of ground-up leaves and rotten wood. Careful measurements of the 

 work of the animals in captivity show that the excrement of the 

 adults amounts to about half a cubic centimeter each per day. It is 

 estimated on the basis of the moist weight of the material that these 

 animals are contributing each year to the fonnation of leafmold at 

 the rate of more than 2 tons per acre. 



The decay of leaves is gi'eatly accelerated also when the under- 

 lying soil is calcareous and alkaline, it being immaterial whether the 

 -148G3°— SM 1913 22 



