Year: 1871

If wick be put in a lamp contain
ing oil, the oil, by capillary action,
gradually permeates its whole length,
that which is above as well as that
below the surface Of liquid. When
the lamp is set burning the oil at the
fame is consumed, and as each parti-
Gle disappears, its place is supplied by
a new one, until the lamp is empty or
the fame extinguished.


Something quite analogous occurs
in the soil, by which the plant is fed.
The soil is at once lamp and wick,
and the water of the soil represents
the Gil. Let evaporation of water
from the surface of the soil or of the
plant take the place of the combustion
of oil from wick and the matter
stands thus: Let us suppose dew or
rain to have saturated the ground
with moisture fer some depth. On
recurrence of dry atmosphere, with
sunshine and wind, the surface of the
soil rapidly dries; but as each parti-
Gle of water escapes (by evaporation)
into the atmosphere, its place is sup
piled (by capillarity) from the stores
below. The ascending water brings
along with it the soluble matters of the
soil, and thus the roofs of plants are
situated in stream of their appropri-
ate food. The movement proceeds in
this SO long as the surface is dryer
than the deeper soil. When by rain
or otherwise the surface is saturated,
it is like letting thin stream of oil
run upon the apex of the lamp wick =
no more evaporation into the air can
occur, and consequently there is 20
longer any ascent of water; on the
contrary. water, by its own weight
peuetrates the soil, and if the under.
!, ing ground be not saturated with
moisture, as can happen where the
subtcrranean fountains yield meagre
supply, then capilIarity will aid gray-
ity i'm its downward distribution.


1t is certain that portion of the
mineral matters, and perhaps also
some organic bodies which feed the
plant. are moro or less freely dissolved
in the water of the soil. So long as
evaporation goes OH from the surface,
so long there is constant upward
flow to these matters. Those portions
which do not enter vegetation accu-
mulate on Or near the surface of the
ground; when rain falls, they are
washed down again to certain deptl',
and thus arc kept constantly changing
their place with the water which is
the vehicle of their distribution. In
regions where rain falls periodically
or not at al, this upward flow of fhe
saltwater often causes an accumuia-
tion of salts on the surface of the
ground.


Thus in Bengal many soils which i'm
the wet season produce the most lux.
uriant crops, during the rainless por-
ton of the year become covered with
white crusts of saltpetre. The beds
of nitrate of soda that are found in
Peru, and the carbonate of soda and
other salts which incrust the deserts
of Utah, ard often fill the air with
alkaline dust, have accumulated in the
same manner. So i'm our western
caves the earth, sheltered from rains,
is saturated with salt-Epsom salt,
Glouber salts and saltpetre, or mix
lures of these. Often the rich soil of
gardens is slightly incrusted i'm this
manner in our summer weather; but
the saline matters are carried into the
soil with the next rain.


1t is easy to see how, in a good soil,
capillarity thus acts in keeping the
roots of plants constantly immersed
in stream of water or moisture that
is now ascending, now descending,
but never at rest, and how the food of
the plant is made to circulate around
the organs fitted for absorbing it.


The same causes that maintain this
perpetual supply of water and food to
the plant, are also efiicacious i'm con-
stantly preparing new supplies of
food. As before explained, the mate
rials of the soil are always undergoing
decomposition, whereby the silica,
lime, phosphoric acid, potash, ETC., OF
the insoluble fragments of rock, be-
come soluble in water and accessible
to the plant. Water charged with
carbonic acid and oxygen is the chief
agent in these chemical changes. The
more extensive and rapid the circula-
ton of water in the soil, the more
matters will be rendered soluble in q
given time, and other things being
equal, the less will the soil be depend
ent on manures to keep up its fertility.
--JohRson's New Work, "HoU Plants
Feed"