Evening star., 1907-08-15
GRASS AND TREES.
Root Surface Of Latter Should Be Free
From Verdure.

hOOt surface OF AaLLeT 0uOulu Do E IcS
From Verdure.
From the Literary Digest.
That many kinds Of trees. especially fruit
trees. flourish better when no grass Is al
lowed to grow over their roots has been
long known to farmers. In some cases the
effect OF the grass on freshly planted trees
is decidedly injurious, and may be almost
fatal This phenomenon has been studied
at the Woburn experimental fruit farm In
England since 1894. and though no perfectly
satisfactory explanation of the action has
been obtained. 1t seems reasonably certain
now that bacteria are concerned in 1t.
Spencer Pickering. who writes on the sub
ject In Nature. tells us that experiment
has shown that 1t cannot be attributed to
the abstraction of food or moisture from
the soil by the grass. nor to the influence
of the grass on the soil temperature or on
the gaseous contents Of the soil. and the
formation of acid or alkali has also been
excluded from the possible causes The
action may be that Of a poison produced
directly by the grass or indirectly through
the agency Of bacteria; or. as appears from
the latest experiments, may be due to the
killing by the grass of root bacteria that
promote growth in some way. The writer
says:
1.-The action Is not confined to any partic-
ular grasses nor to apple trees, but differ
ent grasses and different kinds Of trees act
and suffer. respectively to different ex-
tents. The differences in the results, how
ever, produced by different soils are much
more conspicuous, especially in cases where
trees are not grassed over until a few
years after they have been planted.
Though, the deleterious action Of grass may
generally be noticed throughout the coun-
try, many notable exceptions have been
met with. and these cannot be explained
by any of the patent characteristics OF the
soils In question. Various pot experiments
have been made which emphasize these
observations.
In February last we are told. twenty six
similar trees were planted in pots under
various conditions: seventeen were in soil
or sand which had not been heated and
nine of them In soil which had been ster-
ilized, OF partially sterilized, by heating to
about 200 degrees Z. and TO " degrees T..
respectively (392 and $50 degrees F), the
water lost in the process being made good.
or the seventeen in unsteril1zed material.
all started uniformly at the same time.
whereas of the nine In sterilized soil two
started about two days later. six did not
start until at least fourteen days later and
one has not started yet. To quote further:
."The heating Of the earth. especially to
the low temperature OF 81 degrees. cannot
have appreciably affected It's chemical COM
position and, indeed. the starting Of a tree
into growth Is Independent Of nourishment
supplied to It, as Is shown by the behavior
of trees in sand; the only alteration pro-
duced in the soil by the heating must have
been an alteration in the living organisms
present in It, That bacteria are connected
with root action has. Of course. been es
tablished In certain special cases. but In
these the connection consists OF the bac-
terra being the means OF augmentlng the
food supply of the plant: the present case
Is altogether different for II appears as II
the mere functioning Of the roots was de-
pendent on bacterial action. Such a con-
clusion would be one of far-reaching sig
nificance. OF course. the facts require
much more examination and ton.
but even in their present state they are
sufficiently evident to warrant notification.
That two out of the nine trees In steril-
lied soils showed very little retardation in
activity Is not surprising. as there were
many opportunities for the reinOculation Of
the soil. the pots containing the trees hav-
ing been exposed In the open since Feb
ruary 4, and no attempt having been made
to steriiZe the trees themselves before
planting, though the roots were washed
free from soil. The two exceptional trees
were in earth which had been heated to
the higher temperature; they were two out
of six planted under these conditions. 1t
may also be mentioned that heating to the
lower temperature does not destroy all soil
bacterial indeed. it may increase the total
bacterial contents. 1t Is probably, there
fore a question of killing some particular
bacteria which are connected with root
activity"