110 
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House & G arden 
The Formation of Leafmold 
(Continued from page 108) 
content expressed in terms of calcium 
oxid often reaching 2 to 3 per cent of 
the dry weight. One sample had a lime 
content of 3.SS 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 containing 
2 to 3 per cent of lime is properly re¬ 
garded as a highly calcareous soil. Yet 
such a deposit may be formed in a 
region where the underlying soil is dis¬ 
tinctly non-calcareous, the lime content 
of the soil being only a small fraction 
of 1 per cent and the soil reaction be¬ 
ing 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 derived should 
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. 
It should be understood that the lime 
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 com¬ 
plete neutralization. In all the kinds 
of leaves and herbage thus far examined 
the net result is an acid condition, al¬ 
though lime may be present in large 
amount. Thus in the leaves of silver 
maple a condition of excessive acidity 
exists, about 0.9 normal, notwithstand¬ 
ing the presence of nearly 2 per cent 
of lime. 
As the decomposition of such leaves 
progresses the acid substances are dis¬ 
organized and largely dissipated in the 
form of gases and liquids, while the 
lime, being only slightly soluble, re¬ 
mains with the residue of decomposi¬ 
tion, the black leafmold, and renders 
it alkaline. 
In soils poor in lime, trees and other 
plants constituting the vegetative man¬ 
tle of the earth may be regarded as ma¬ 
chines for concentrating lime at the 
surface of the ground. This lime is 
drawn up by the roots in dilute solu¬ 
tion from lower depths, is concentrated 
in the foliage, and the concentrate is 
transferred to the ground by the fall and 
decomposition of the leaves. The pro¬ 
verbial agricultural fertility of the vir¬ 
gin timberland of our country was un¬ 
doubtedly 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 de¬ 
composed. 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 en¬ 
sued, which, for the purposes of ordi¬ 
nary agriculture, could be remedied only 
by the artificial application of lime. 
Active Agents of Decay 
The chief agents in the decay of leaves 
are undoubtedly fungi and bacteria. 
There are other agencies, however, that 
contribute greatly to the rapidity of 
decay. Important among these are 
earthworms, larva of flies and beetles, 
and myriapods or thousand-legged 
worms. Animals of all these groups 
exist in myriads in the leaf litter. They 
eat the leaves, grind them, partially de¬ 
compose them in the process of diges¬ 
tion, and restore them again to the soil, 
well prepared for the further decom¬ 
posing action of the microscopic organ¬ 
isms 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 contributing to the formation of leaf- 
mold has not been adequately recog¬ 
nized. In the canyon of the Potomac 
River, above Washington, on the steeper 
forested talus slopes, especially those 
facing northward, the formation of al¬ 
kaline leafmold is in active 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 opposite Plummers 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 myria¬ 
pods, the largest and most abundant 
being a species known as Spiro bolus 
marginatus. The adults are about 3" 
in length and a quarter of an inch in 
diameter. They remain underneath the 
leaves in the daytime and emerge in 
great numbers at night. On one oc¬ 
casion a thousand were picked up by 
Mr. H. S. Barber on an area 10' x 100', 
without disturbing the leaves. On an¬ 
other occasion an area 4' by 20' yielded 
320 of these myriapods, the leaf litter 
in this case being carefully searched. 
Everywhere 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 formation of leafmold at the 
rate of more than 2 tons per acre. 
On Oakaline Soils 
The decay of leaves is greatly ac¬ 
celerated also when the underlying soil 
is calcareous and alkaline, it being im¬ 
material whether the lime is derived 
from a limestone formation or is a con¬ 
centrate of the vegetation. On the rich 
bottom-land islands of the upper Poto¬ 
mac the autumn leaf fall barely lasts 
through the following summer, so rapid 
is its decay. These bottom lands have 
an alkaline 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 prompt 
neutralization of the acid leachings of 
the leaves and also to the fact that 
such a substratum harbors with great 
efficienc) 7 many of the most active or¬ 
ganisms of decay, from bacteria to 
earthworms. 
It must not be understood that in 
a state of nature the decomposition of 
leaves is always so simple and uniform 
a process as has been described, or that 
it always results in the formation of 
an alkaline leafmold. The chief factors 
that contribute to the acceleration of 
leaf decay have already been enumer¬ 
ated, but there are other conditions of 
nature that obstruct and retard this 
process. Under certain conditions the 
progress of decomposition may be per¬ 
manently suspended long before the 
alkaline stage is reached. The soils thus 
formed, although high in humus like 
a true leafmold, have an acid reaction 
and a wholly different flora. 
A Correction 
Through an error, the caption under 
the photograph on page 39 of the Sep¬ 
tember issue of House & Garden cred¬ 
ited the dining room there shown to 
the house of Charles Wimpjheimer, Esq., 
of which Harry Allen Jacobs was archi¬ 
tect. The room is actually in a resi¬ 
dence at Rye, New York, designed by 
Hobart B. Upjohn, architect. Other 
views of this residence will be shown 
in a future number .— Editor. 
