82 coville: formation of leafmold 



progress. The purer deposits are found in pockets among the 

 rocks, where the leafmold is not in contact with the mineral 

 soil and does not become mixed with it. The slope directly oppo- 

 site Plummer's Island is a good example of such localities. Here 

 during all the warm months the fallen leaves of the mixed hard- 

 wood forest are occupied by an army of myriapods, the largest 

 and most abundant being a species known as Spirobolus margin- 

 aius. The adults are about 3 inches in length and a quarter of 

 an inch in diameter. They remain underneath the leaves in the 

 day time and emerge in great numbers at night. On one occa- 

 sion a thousand were picked up, by Mr. H. S. Barber, on an area 

 10 by 100 feet, without disturbing the leaves. On another occa- 

 sion an area 4 by 20 feet yielded 320 of these myriapods, the leaf 

 litter in this case being carefully searched. Everywhere are evi- 

 dences 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 formation of 

 leafmold at the rate of more than two tons per acre. 



The decay of leaves is greatly accelerated also when the under- 

 lying soil is calcareous and alkaline, it being immaterial whether 

 the lime is derived from a limestone formation or is a concentrate 

 of the vegetation. On the rich bottomland islands of the upper 

 Potomac the autumn leaf fall barely lasts thru the following 

 summer, so rapid is its decay. These bottomlands have an alka- 

 line flora, and they are found to have an alkaline reaction, caused 

 by the lime brought to them in the flood waters. 



The acceleration of leaf decay by an alkaline substratum is 

 due to the prompt neutralization of the acid leachings of the leaves 

 and also to the fact that such a substratum harbors with great 

 efficiency many of the most active organisms of decay, from bac- 

 teria to earthworms. 



It must not be understood that in a state of nature the decom- 

 position of leaves is always so simple and uniform a process as 

 has been described, or that it always results in the formation of 



