332 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
April 18, 1896. 
PLANT-FORMING ELEMENTS. 
The plant-forming elements have been divided by agri-horti- 
snltnrist chemists in two classes ; (1) The organic elements, or 
ihose which appear destructible by fire; (2) Inorganic elements, 
(&T those which after combustion remain as a residue or ash. These 
sr© but general terms, for chemists recognise an element as organic 
®r inorganic according as it is or is not a part of an organised body. 
^Nevertheless, the plant-forming elements naturally fall into two 
gToaps, and are marked by clearly defined and widely different 
abaracteristics. The first of these elements is derived exclusively 
iFrora the air, and the second furnished wholly by the soil. These 
iwo distinctive classes of elementary substances enter into the 
©omposition of plants, and both are equally essential to their life 
3nd growth. 
The elements derived from the air are carbon, hydrogen, oxygen, 
argon, and nitrogen. These are the chief constituents of plants, 
forming from 95 to 99 per cent, of their entire weight, and in 
ja'oeess of burning pass off into the atmosphere in the form of 
gases. It is clear, therefore, that plants must derive the organic 
©lemeats directly from the atmosphere in gaseous form, but it must 
not be supposed that the air-derived elements are always obtained 
directly from the air, for the amount of organic substances present 
in i^e soil, especially when highly cultivated, is considerable, as the 
air-derived elements there combine with inorganic substances to 
form chemical compounds, and as such are imbibed bv the roots of 
plants. 
The organic elements enter plants by the roots in combination 
yith the inorganic in the form of sulphates, phosphates, nitrates, 
ansi chlorides of potassium (potash), calcium (lime), magnesium 
{magnesia), and iron. These salts® enter plants by the absorbent 
surfaces of the roots, pass upwards through the stems to the leaves 
and new-forming buds, and the leaves gather carbon dioxide gas 
from the air, which is decomposed under the action of the sun’s 
light ^ its carbon remains in the plant, and the oxygen, or very 
nearly an equivalent quantity, is given off into the air again. By 
nosans of the carbon so acquired, and the elements derived with 
water from the soil, the plant is able to organise the carbohydrates, 
their formation proceeding in the chlorophyll cells, and the first 
product detected by the microscope is the starch granules ; but 
chemically the glucoses are the first products of the synthesis. 
The albuminoids cannot be produced without nitrogen, and 
rery Tittle of that is derived directly from the atmosphere ; indeed, 
it is practically unassimilable by plants. Even the atmospheric 
nitrogen largely collected by leguminous plants is inappropriable by 
them until converted by a micro-organism of the bacterial class 
into assimilable matter ; therefore, plants derive their supplies of 
nitrogen from the soil in the form of nitrates or salts of nitric 
acids. Fats, alkaloids, and acids are built up from the same food 
elements. The steps in the construction of organic matters are, 
in most eases, unknown or of uncertain conjecture. All we know 
for certain is that the carbohydrates and albuminoids are organised 
in^ ine leaf, transformed into its substance, and thence trans¬ 
mitted to every living cell of the plant, which has, within certain 
ijEDjts, a power of selecting its food, preference being given by 
most to potash before soda. Even seaweed contains more potash 
iian soda, yet sea water contains twenty-five to thirty times more 
of the latter than the former. Notwithstanding, plants cannot 
wioby reject substances that are of no use or even poisonous to 
them. Plants, however, are seldom poisoned by rejected matter, 
as cultivated soils, by the influences of aeration, chemical and 
physical qualities, render such more or less insoluble, consequently 
proportionately innocuous. 
The atmosphere is practically invariable in its composition, 
hence its functions are essentially the same towards plants. The 
30 j 1, on the other hand, is variable in composition, and has offices 
pfcnhar to itself. Thus it can be improved and enriched, and in 
Eoasequence of a certain plant appropriating a given element 
larger than another it may be deteriorated or exhausted. 
^ Crops cannot derive appreciable amounts of the elements found 
iffl their ash from the atmosphere, but the soil may accumulate the 
air elements by the waste of crops and animals, such as carbon 
dioxide and nitrogen, the last being chiefly supplied to plants by 
soil, which is formed therein as nitrates from various sources 
while the ammonia salts supply nitrogen to vegetation. Hydrogen 
ana oxygen are supplied in the water which the roots of plants 
imhibe; indeed, it is from the soil that the plant gathers all the 
water it requires, and is the vehicle by which it receives the soil- 
aeriTed elements, being the fluid medium of its chemical and 
iii'sctural transformations. 
The elements furnished to plants exclusively from the soil are : 
iSon-metals sulphur, phosphorus, silicon, and chlorine ; metals— 
v£3.4tothe%Towthof™aute!' u«iesseutial, from a minuriU point of , 
potassium, sodium, calcium, magnesium, iron, and manganese. 
These soil-derived elements all occur in plants in small proportions, 
and vary in amount from a fractional part of 1 per cent, to 10 or 
12 per cent., but though the proportions are small, they, or some 
of them, are as important as the more abundant organic elements ; 
indeed, both are equally essential in the formation of plant 
tissue. The inorganic substances of plants are ascertained by an 
analysis of the ash of the respective species or variety, the mineral 
matter remaining as residue when plants are burned. But the 
combustion is always more or less incomplete, so that in the ash 
there remains minute amounts of carbon, oxygen and nitrogen, 
and slight traces of chlorine, phosphorus, and sulphur are known 
to be given or dried off in the heating, yet the amounts are very 
small in either case. An analysis of the ashes of a plant therefore 
affords a safe guide as to its requirements of soil and manure, and 
that of the whole elements known to chemists not more than one- 
fifth are needed by plants for the building up of their structures. 
Four—carbon, oxygen, hydrogen, and nitrogen—of the fourteen 
elements are derived directly or indirectly from the air, and con¬ 
stitute over 90 per cent, of all vegetation, consequently the 
atmosphere is a sort of aeriform food-supplying medium, which 
plants imbibe as gases, yet these air-derived elements are not more 
important factors in vegetable nutrition than the soil-derived 
substances that occur in much smaller amounts, for both are 
essential to the healthy development of plants, and of equal 
importance in plant economy. 
Over the air-derived elements the cultivator has practically no 
control in outdoor culture, and it is doubtful if ammonia in glass 
structures has any more than a fancied beneficial effect upon 
vegetation. Of course, all growers know that decomposing matter, 
such as leaves, cocoa-nut fibre refuse, mulchings of manure, and 
even sprinklings of liquid manure, produce atmospheric conditions 
more or less beneficial to vegetation, but whether this is due to the 
gases evolved or the uniform hygrometrical state of the atmosphere 
is not determined beyond uncertain conjecture. Free nitrogen 
is of no use whatever to plants, not even to leguminous, but 
vegetation assuredly profits by the ammonia and nitric acid in 
rain water, yet who can tell how these in fluid form can enter 
plants other than through the roots ? Epiphytes certainly 
appropriate the ammonia and nitric acid of the atmosphere, but 
it is by their aerial roots, not the leaf surfaces. 
Nitrogen in the soil, or in a fertiliser, is never present in the 
form of nitrogen gas, but exists in combination with some other 
element or elements, yet chemists in their analyses determine, 
without regard to the form, how much this combined nitrogen 
would amount to if it were present in the form of pure nitrogen 
gas. It may be in the form of ammonia, as sulphate ; in the form 
of organic nitrogen, as in animal or vegetable substances ; or in the 
form of nitrate, as nitrate of lime, potash, or soda. Ammonia is a 
compound formed by the chemical union of nitrogen with hydrogen, 
fourteen parts of nitrogen uniting with three parts of hydrogen to 
make seventeen parts of the element called ammonia, consequently 
1 lb. of nitrogen will make 1‘214 lbs. of ammonia. Each pound 
of ammonia contains a little less than two-tenths of a pound of 
hydrogen, and this has value only in that its combination with 
nitrogen forms a compound more readily assimilable by plants. 
Hydrogen is present in all animal and vegetable substances, and 
forms an essential constituent of acids. It combines with oxygen 
to form water, of which it forms one-ninth by weight, being the 
lightest of all known substances. Atmospheric air is about fourteen 
and a half times heavier than hydrogen, but by its combination 
with oxygen it enters the plant in the soil waters, and its property 
is to make plant food more easily assimilable. 
Nitrogen constitutes about four-fifths of the bulk of the earth’s 
atmosphere, and in its free condition manifests no positive or 
active properties. Plants cannot live if confined in an atmosphere 
of nitrogen gas. The nitrogen and oxygen of the air are a mere 
mechanical, not a chemical, mixture, the nitrogen assumedly 
modifying the action of the energetic oxygen. Although nitrogen 
is an essential and constant constituent of plants, and the atmo¬ 
sphere a great reservoir of this element, there are few plants that 
can appropriate it from the atmosphere, and it would not be of 
any use to them without the intervention, within the tissues, of 
certain micro-organisms, which convert it from free into assimilable 
nitrogen. This element is also present in soils, but it exists in 
these in a comparatively inert and useless state. The humus of 
soils is a source of nitrogen, peat often containing 2 or .3 per cent. 
Of this nitrogen, as gas, plants can make no use, for it is only the 
nitrogen, combined with other elements or their compounds, that 
is assimilable by vegetation. As such nitrogen exists in soils and 
in the form of nitrates, compounds of ammonia, or combined with 
organic matter, and of these the chief source of immediately 
available nitrogen is the nitrates, then the ammonia, and very 
slowly that of organic matter. 
