BROOKLYN BOTANIC GARDEN 
LEAFLETS 
Series VII Brooklyn, N. Y., October 15, 1919 No. 8 
THE LIVING SOIL 
It is really very much alive. A single teaspoonful of it may con- 
tain as many as 25,000,000 or more germs of various sorts (bacteria, 
molds, protozoa, etc.) A fertile soil especially, well provided 
with humus, is teeming with life; indeed, it must contain these 
living organisms in order to be fertile and to support plant life. 
“Mother Earth,’’ of Greek mythology, is really a good name after 
all, for besides being very much alive, she is the bounteous 
provider of food, and thus the mother of mankind, as well as of 
all living things. 
The soil, then, is not a lifeless lump of clay. When well tilled, 
it is full of pores like a sponge; and when in the best condition 
for plant growth, these pores contain an abundance of air as well 
as water. We may thus think of the soil as a honey-combed, 
spongy mass, made up of a hard framework composed of bits of 
mineral matter, the rock-particles, plastered over with a jelly-like 
substance (the decaying organic matter, or “humus”), contain- 
ing countless billions of bacteria and other germs. 
The great majority of these living organisms are present in the 
surface soil, where the humus is, and where the tilling of the soil 
has provided the porous, well-aerated condition necessary for the 
growth of the beneficial germs. 
Further, their activity is greatest as a rule in late spring and 
in autumn, and lowest in summer and winter. For the wintercold 
checks them, as well as the summer dryness. The warming of 
the soil in spring, together with the spring rains, bringing an 
abundance of oxygen washed down out of the air, as well as the 
needful water, apparently cause the great outburst of germ act- 
ivity in late spring. The autumn maximum may be attributed to 
the effect of the fall rains coming after the heat and drought of 
the summer. 
There are both good and bad soil organisms. Some bring about 
the decay of plant and animal remains and the consequent liber- 
