178 NATURAL HISTORY OF THE FARM 
such leaves will be found. Commingled with the leaves are 
pieces of stems and bark and twigs. Strips of birch bark 
long persist, being rendered well-nigh moisture-proof by 
their abundant resin. 
Under the recognizable leaves and twigs is humus, formed 
from those that fell earlier. It is black and full of moisture. 
It is mingled with the top layers of the soil. As we uncover 
the floor of the leaf-beds, we see some of the agents nature 
uses in promoting the formation of humus: molds and 
mildews and other fungi of many sorts. that grow in and dis- 
integrate the plant-stuffs; snails and earthworms and mille- 
pedes and pill-bugs and spring-tails and many insect larve 
that eat them. Carnivores are here, also; ground-beetles 
and centipedes and spiders, among the lesser forms, and 
salamanders and shrews, among those of larger size. The 
beds of leaf-mold have a population of their own. All are 
hastening the restoration of the useful plant materials to the 
soil. Numberless roots are holding the humus together. 
They never let go; this is nature’s way of keeping the soil 
productive. It is only after we have dug down through the 
humus-stained top layers thet we come to soil that looks 
like that in the fields. 
Not in the woods alone, but also in the wild meadow and 
on the prairie, nature practices admirable economy in the 
use of her soil-riches. Gravity aids in the enrichment of 
the lowlands, but in spite of gravity the soil of the hills 
improve as time runs on and wild crops grow upon them. 
In holding what is gained the deep-rooting forest-cover is 
not more useful than is the turf-forming ground-cover her- 
bage. Great and small are colaborers in nature’s plan. 
Her method is conservation with use—the fullest possible 
use—the use that brings the greatest good to the greatest 
number, and that insures the continued welfare of a teem- 
ing population. 
