Atlanta semi-weekly journal. (Atlanta, Ga.) 1898-1920, 1912-01-26

Vegetation begins with the very
simplest forms OF plants. such as
Hchens and MOSES. and is, OF course
very scanty at first. These plants on
dying become a part OF the soil. all
sf the plant nutrients used by them be-
Ing thus returned
Food that has once been used BY
plants is very readily made available
to succeeding crops through the pro-
cess OF decay. The soil is Ow able
to produce a larger crop. as IL con-
b-sas the plant food in the previous
growth in addition to that added
through the agencies detailed above
In this way the growth gradually be-
comes more abundant The plants upon
decayfng give rise to humus. and this
increases TIE fertility OF the land both
by being a source OF plant food and by
increasing the wster-retaining power.
Humus is a very important factor IN
fertility. During the decomposition 81
the plants, acid substances are formed
which act upon the rocks in such way
as 70 make more Of the plant food
available.
One OF the products OF decay OF fer
mentstfon Is carbonic acid gas. and this
is dissolved in the soil water, and this
gas-containing water is an important
help in disintegrating the rocks
As the nutritive materials increase
from thes evarious caluses the lower
simpler forms OF plant life are grad
uaIly replaced by those which are more
highly organized
With the advent OF plants. like our
common crops. which bear roots, other
factors In the formation OF soils are
introduced. The roots secrete an acid
substance that has a solvent effect on
the mineral matter OF the soil. and the
roots themselves also assist mechanl-
caIly in breaking down the rocks
All are familiar with the tremendous
force exerted BY plants in breaking
apart rocks and stones IL once their ten
der rootIets obtain a foothold in a crew
ice.
The roots penetrate the soil some
times 10 great depths. and. as they de-
cay after the death Of the plant, they
leave little channels in the soil which
serve TO carry down water laden with
carbonic acid, as well as TO introduce
the oxygen OF the air. that. in its turn,
Is q factor IN bringing about chemical
changes in the soil, which assist in
making plant food available.
Sooner or later In the process OF soil
formation, plants OF the pulse family,
Oeguminous plants. such as clover,
vetches. lupines. etc, are introduced
II you dig up some OF these plants
you viii ind litsle nodules or tubercles
OF their roots. These noduies are the
homes OF numerous bacteria. which en-
able the plants 20 derive part OF their
food from the nitrogen OF the atmos-
pierre
This peculiar property OF leguminous
plants IS OF great Importance. for II Is
undoubtedly natures principal method
OF increasing the supply OF nitrogen in
the ground.
The nitrogen compounds accumulated
BY these plants eventually become a
part OF the soil through their decay.
thus adding 70 its fertility.
II win readily be understood that the
various agencies concerned in the form
alton OF the soil do not act separately
nor necessarily in any such order as
that IN which they have been discussed.
As q matter OF fact all the processes
described take place simultaneously. The
lower plants do not wait for the rocks
20 be pulverized. for we see such organ
isms as the Hchens growing on rocks
from which one would think ft impos-
sible 20 obtain food.
II the Mchen Is removed. grooves or
burrows will be found on the surface OF
the stone. due 70 the action of the
plant
Nor are al soils formed directly from
the original rocks. for one OF the ef-
fleets OF weathering, etc. is TO separate
such rocks as the GRANTEES into simpler
substances. with the result, for exp
ample. that huge deposits OF limestone