526 
NATURE 
[ Sept. 30, 1886 
quantity, each of the particles becomes clothed with a 
layer of water, and some of the air is driven out, though 
bubbles of air will still exist in the larger interspaces. 
A third case is conceivable—so much water might be 
supposed to find its way in, that no air remained in the 
interspaces between the particles of soil. Now it is true 
that such a state of affairs is not readily brought about in 
a normal soil; but I may indicate how the result is occa- 
sionally attained to a great extent. Suppose that a layer 
of clay or other impenetrable subsoil lies beneath the soil 
in question ; then if water oozes into the soil in larger 
quantities than can be got rid of in the time, it is possible 
for nearly all the air to be displaced. Of course the 
object of good drainage is to prevent this ; and it is often 
overlooked that drainage from below has the effect of 
drawing in air as well as of running off superfluous water 
—air is driven into the spaces as the water leaves them. 
In speaking of the “bubbles of air” entangled in the 
interspaces between the particles of soil, each with its 
water-blanket, I have overlooked some details as to what 
the bubbles really are. Asa matter of fact they will not 
remain of the same composition as ordinary air, and may 
soon differ considerably ; besides the vapour of water, 
they may contain gases in quite different proportions from 
those in the air outside. In. the type case, however, there 
will be some oxygen present in the bubbles. 
It is not intended here to go very fully into a descrip- 
tion of the structure of the roots of land-plants ; enough 
if you are reminded how the smaller ramifications of a 
root are found to be more numerous and thinner as we 
approach the periphery of the mass of earth which they 
traverse. From the youngest rootlets are produced the 
root-hairs, in enormous quantities, new ones arising 
forwards— Ze. near the tip of the rootlet-—as the rootlet 
grows on, and those behind dying off after fulfilling their 
functions. These functions are chiefly to apply themselves 
in the closest manner to the surfaces of the particles of 
soil, and in this way to place the water which they 
contain in direct continuity with the water which clings 
with such enormous force to the surfaces of the particles. 
Hence this water can pass from the soil to the plant, and 
anything dissolved in the water can also pass into the 
root-hair and thus up into the plant. 
I am not going to dwell on how the root-hairs them- 
selves aid in dissolving mineral substances—corroding 
the surfaces of the particles of soil they cling to—nor 
shall I trouble you with the details of what substances 
will be dissolved in the water ; for, of course, you will see 
that anything soluble will pass into solution and may be 
carried into the plant. 
The chief point to be insisted on just now is that this 
water in the soil will contain among other substances 
oxygen dissolved in it from the air-bubbles referred to 
above, and that this dissolved oxygen will pass into the 
root-hairs in solution together with the minerals and any 
other substances. This oxygen, moreover, is absolutely 
indispensable for the life of the root-hairs ; it can be easily 
shown that if the supply of oxygen is stopped, cr even 
diminished to any considerable extent, the roots begin to 
die, because the root-hairs cease to act. 
Let us look a little more closely into this point. Each 
root-hair is a tiny cell containing living protoplasm and 
certain other substances, all inclosed in a thin, elastic, 
porous membrane. Now it has been abundantly proved 
that if such a cell is deprived of oxygen, its protoplasm 
becomes dormant for a time, and slowly breaks up, as it 
were ; subsequently it becomes decomposed into other 
and simpler materials. A sort of internal combustion 
and fermentation take place, and these processes result 
in the formation and liberation of bodies like carbon- 
dioxide, alcohol, acetic acid, and other acid matters— 
substances in the main not only incapable of supporting 
the life of the root-hairs but actually destructive of it. 
{ 
oxygen, they will eventually die. Their death will entail 
that of the rootlets and roots to which they belong, and 
this for two obvious reasons—first, it is the root-hairs and 
the root-hairs alone which can absorb the necessary water 
and substances in solution from the soil to supply such a 
plant as we are concerned with; and, secondly, the 
noxious products resulting from their death accumulate in 
the soil and diffuse into the root, and so hasten similar 
decompositions in what were hitherto healthy cells. 
It must not be supposed that these disastrous conse- 
quences of the deprivation of oxygen always follow imme 
diately. Not only are the roots of some trees, for instance, 
able to withstand ill-treatment longer than others, but, 
obviously, the kind and degree of ill-treatment may 
affect the problem of how long the plant shall survive. 
The number of rootlets and root-hairs, and the spread of 
the roots and other factors, will obviously affect the 
matter. 
Suppose the following case as an example. A young 
tree is growing and flourishing in an open, good soil, and, 
for some reason or other, more soil is heaped about the 
roots until the depth is increased considerably: the 
deeper situation has placed obstacles in the way of the 
roots obtaining oxygen so readily as before. Not only 
are the roots further from the atmosphere, but the water 
carried down has to percolate through more soil, and may 
part with much of its oxygen (or even all) on the way : 
of course the nature of the soil, the presence of organic 
matters, and other circumstances decide this. It is not 
at all difficult to conceive of such a case where the supply 
of oxygen to the roots is thus diminished so far that the 
activity of the root-hairs as a whole is simply lowered, 
but not destroyed,—a stage or two further and they might 
become dorment, and their protoplasm undergo intra- 
molecular respiration for a time, and break up. It is 
clear that the diminished activity of the roots will affect 
the supply of water (and the substances dissolved in it) to 
the leaves : this will obviously react on the thickness of 
the annual rings, and this again on future supplies—since 
the water passes up the alburnum or young outer layers 
of woody tissue. Moreover, a diminution of supplies 
from the leaves means less substance and power for re- 
placing the root-hairs, and so on, In this way it may 
require some time to kill the tree, and all kinds of com- 
plications may arise meanwhile. This case is probably 
by no means unconimon. 
A more extreme case is where the soil becomes damp 
and clogged with excessive moisture: not only does 
no oxygen reach the roots, but noxious gases accumulate 
in solution in the soil, and will hurry matters by poison- 
ing cells which might otherwise live a longer life of use- 
fulness. It is extremely probable that such gases find 
their way into higher parts of the plant in the air-bubbles 
known to exist and to undergo alterations of pressure in 
the vessels of the wood: this being so, they would slowly 
retard the action of other living cells, and so affect the - 
upper parts of the plant even more rapidly than would 
otherwise be the case. Damp soil may thus do injury 
according to its depth and nature ; but it need not neces- 
sarily be deep to be injurious if much oxygen-consuming 
substance is present. I have seen excellent soil converted 
into damp, stinking, deadly stuff from the action and 
accumulation of the larvee of cockchafers ; these “ grubs” 
may, it is true, accelerate the devastation caused by the 
consumption of oxygen and the accumulation of poisonous 
waste matters in the soil by directly cutting off portions 
of the roots themselves, but the accumulation of oxygen- 
consuming substance, and the cutting off of supplies to 
the root-hairs evidently plays a chief part in the destruc- 
tion. 
There is another matter with regard to damp soils 
that cannot be left out of account. I have already told 
you that roots which are developed in water or in very 
Evidently, then, if we deprive all the root-hairs of | damp sandy soil—and which are perfectly healthy—have 
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