Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS AND SOLUTION FOR PRESERVING GREEN PLANT TISSUES
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FIELD OF INVENTION
This invention relates to the preservation of green
plant tissues and more particularly to a novel composition of
matter for the preservation of the natural green colour in
leaves, stems and the like of flowers, shrubs, trees and the
like and the preserved product.
Background of Invention
In our earlier Canadian Patent 1,103,475 issued
June 23, 1981 and assigned to the assignee of the present
invention, there is described a process and composition of
matter for preserving green coloured plant tissue while
retaining the natural green colour thereof, in which the
tissues are immersed in a solution comprising 30-70% by
volume water; at least one monohydric alcohol; at least one
preservative component selected from the group comprising
lower carboxylic acids, and di and trihydric alcohols, and
sufficient bufEering and mordant reagents to control the pH
and osmolality of the solution so as to permanently retain
the green colour in the tissues. While this solution
produces generally satisfactory results for almost all kinds
o green leaves, it is somewhat expensive to produce as it
is relatively concentrated. We have now found that relatively
more dilute solutions than heretofore employed may be employed
with equally good results, provided the compositions contain
relatively larger quantities of cupric salts than heretofore
employed.
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Brief Description of Invention
Thus, by one aspect of this invention there is provided
a process for preserving naturally green coloured plant tissues
comprising immersing said tissues in a solution comprising
about 70 - 90~ by volume water
5 - 20% by volume of a monohydric alcohol
5 - 15% by water sulphurous acid
and containing 15 - 25 gms cupric chloride
20 - 30 gms cupric sulphate
and 5 - 12 gms citric acid
per litre of solution, for a sufficient time to effect exchange
of water naturally contained in said tissues with said solution,
thereby biologically preserving and fixing the green colour
in said tissue.
Detailed Descri~_on of Invention
The preservation oE green plant tissue æpecimens is
considerably more difficult than preservation of relatively
fibrous flowers and the like. Firstly, the cellulose and
similar materials in green plant tissues form a relatively
rigid framework into which the cells are arranged. The cells
are, however, fully turgid only when filled with water and once
this water is lost they collapse and the weight of tissues is
too great for the relatively small amount of fibre to support
When this happens wilting occurs when the tissue dries out
completely, rigidity is restored due to the loss of weight and
the loss of lubrication between fibresu In succulents there
is so little fibre that complete dehydration and rigidity is
almost impossible to achieve. The dehydration process must
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be complete before the tissue i5 removed from its physical
supporting medium. Failure to ensure this results in loss of
shape and chemical reactions which ultimately result in tissue
discoloration. Secondly, the green coloration is due to the
presence of chlorophyll which is a highly reactive and sensitive
substance, and unless considerable care is taken with the de-
hydration process, degradation of the chlorophyll occurs. It
is therefore necessary to effect dehydration in such a way as
to retain the original colour and shape substantially intact
and subsequently treat the dehydrated tissue with a preservative
to make it last.
As discussed in our related application, we have
found that rather than dehydrate leaves or other green plant
tissue and then preserve the dried tissues, it is preferable to
efEect an exchange process wherein the naturally contained water
in the tissue is exchanged with a water based treatment solution
containing sufficient chemical reagents to biologically preserve
and environmentally fix the green colours. Buffers and the like
may be addad to modify the effects o the primary chemicals.
Thus, it has been found that a suitable treatment
solution for green plant tissues mu~t contain four essential
groups of chemicals which may be defined as:
(a) water;
(b) an exchange medium,
(c) preservatives; and
(d) buffers, mordants and modifiers.
Throughout this specification, when reerring to
"water" it is implicit that distilled water is normally employed,
in order to ensure uniformity or results and to provide a readily
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controlled standard, but it will be appreciated that distilla-
tion is not an essential characteristic of the water employed,
other forms such as deionized water being equally effective.
The "exchange medium" used in the present inventions is normally
one or more monohydric alcohols containing 1 6 carbon atoms.
Such alcohols, particularly ethyl alcohol, isopropyl alcohol
and tertiary butyl alcohol are known to have considerable de-
hydration properties and, without wishing to be bound by this
explanation, it is believed that in the present invention the
alcohol or mixtures of alcohols selected causes dehydration of
the natural water contained in the plant tissue and the simultan-
eous replacement thereof by the chemical-containing water of the
inventive solutions of the alcohols listed, tertiary butyl
alcohol is extremely harsh and may damage leafy tissue and for
this reason is normally used in admixture with a milder alcohol
such as l-propanol. Ethyl alcohol, on the other hand may be
used alone.
The preservative elements include biological preser-
vatives and fixers and environmental fixers, such as sulphurous
acid.
The buffers, mordants and modiiers include citric
acid and cupric salts such as cupric chloride and cupric sulphate.
The amounts of each chemical required depends upon the type of
leaf being treated, the exchange medium being used and other
factors. Some chemicals appear to act as colour mordants while
others are buffers not only for pH but also for osmolality. The
pH range is not considered critical and although the bath i5
generally maintained in the range 6-8, i.e. substantially neutral,
pH as low as about 2 may also be employed.
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Preferred treatment solutions comprise (in amounts
per litre of solution):
700 - 900 ml water
20 - 30 g cupric sulphate
15 - 25 g cupric chloride
5 - 12 g citric acid
50 - 200 ml ethyl alcohol
50 - 150 ml sulphurous acid,
and more particularly
800 ml water
25 g cupric sulphate
20 g cupric chloride
lO g citric acid
100 ml ethyl alcohol ~-
100 ml sulphurous acid.
The procedures to be adopt:ed for treatment of the
plant tissue are simple and straightforward. Firstly a treating
solution is prepared by mixing the r~!quired chemicals, preferably
in the order as noted below, and then immersing the specimens in
; 20 the treating solution, at ambient temperature, for 10 days to
2 weeks or even longer depending upon the specimen. For example
most deciduous leaves require a relatively shorter period of time
than evergreens and thick tough leaves such as holly may require
as long as 30 days or even more. Very thick leaves, for example
rubber leaves, may require even lon~er. Leaves of succulents
and other species which tend to be very watery and with little
fibrous structure (for example water cress) by reason of their
species or method of culture are somewhat difficult to treat
according to the present invention even if great care is taken
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with the selection of the exchange medium as it appears difficult
to balance the rate of exchange of natural water with the treat-
ing solution. Generally, upon immersion in the bath the colour
of the leaves changes, usually to a lighter green, then as the
treatment solution replaces the natural water the colour reverts
to an "ideal" colour and on continued immersion the colour
darkens. Following treatment in the treating solution, the
specimens may be air dried and stored for use as required. Such
treated specimens are best used ~for teaching or similar purposes)
within 2 to 3 weeks as they tend to dry out aftex that time. If
it is desired to pre~erve the specimens for later use (i.e. spring
or summer leaves for usP as teaching aids in mid winter) or for
permanent display, a secondary treatment in a "holding solution"
is required. The holding solution is a glycerin/water solution
preferably containing 100-700 ml glycerin per litre of water.
The specimens are merely immersed and soaked in the holding
solution for 2-3 weeks, at ambient t:emperature and then air dried.
Specimens so treated maintain their colour and flexibility for
periods in excess of 1 year. In certain circumstances it may
be desirable to store the specimens permanently in the holding
solution, depending on the end use. There is, therefore, no
practical limit to the treatment time in the holding solution~
Example 1
A series of green leaf samples, as set forth in Table
1 below were immersed in a solution comprising 800 ml water,
100 ml ethyl alcohol, 100 ml sulphurous acid, 25 g cupric
sulphate, 20 g cupric chloride, and 10 g citric acid or periods
varying from 10 days to 2 weeks at ambient temperatures. After
treatment the leaves were placed in a holding bath containing
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650 ml white glycerin per 1000 ml distilled water for 2-3
weeks, then removed, air dried and evaluated for colour and
Elexibility.
Table I
Specimens Results
whi~e spruce good
balsam good
geranium fair
holly good
sugar maple good
silver maple good
birch good
white cedar good
greenhouse fernsgood
junipers good
red oak good
basswood good
cat-tails good
beech good
flowering crab good
elm good
