Note: Descriptions are shown in the official language in which they were submitted.
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PRESERVATION OF GREEN PL~NT TISSU~S
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 THE INVENTION
In our earlier Canadian Patent 1,103,~75 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 tissues 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 buffering and mordant reagents to control the pH
and osmolality of the solution so as to permanentl~ retain
the green colour in the tissues. Within this general
description of the treatment solutions which is suitable for
almost all kinds of green leaves, we have found that certain
tissues such as ferns, grasses, lichens, mosses, salal, and
certain coni~erous needles are best treated with modified or
special solutions particularly formulated for their special
requirements.
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BRIEF DESCRIPTION OF INVENTION
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By one aspect of this in~ention there is provided
a solution, for the preservation of naturally green coloured
plant tissues, consisting essentially of: 35-45~ by volume
water; 20-30~ 2-propanol, 5-12~ propionic acid, 5-10% sulphur-
ous acid, 5-10~ formalin, 2.5-5% formic acid, 1-5% ethylene
glycol, a selected amount of (a) at least one cupric salt
selected from the group consisting of cupric sulphate, cupric
chloride, cupric carbonate, cupric acetate and cupric nitrate,
(b) citric acid, (c) sodium phosphate, (d) sodium sulfite,
(e) DBE, (f) 20-20-20 fertilizer, (g) magnesium sulphate
(h) glycerol, (i) butylated hydroxytoluene.
By another aspect there is provided a process for
preserving naturally green coloured plant tissues comprising
immersing said tissues in a solution comprising: 35-45% by
volume water; 20-30% 2-propanol; 5-12~ propionic acid; 5-10%
sulphurous acid; 5-10% formalin; 2,5-5% formic acid; 1-5~
ethylene glycol; a selected amount of (a) at least one cupric
salt selected from the group consisling of cupric sulphate,
cupric chloride, cupric carbonate, cupric acetate and cupric
nitrate, ~b) citric acid, (c) sodium phosphate, (d) sodium
~ulphite, (e) ~ibasic ester, ~f) 20-20-20 fertilizer, (g) mag-
nesium sulphate, (h) glycerol, (i~ butylated hydroxytoluene.
DETAILED DESCRIPTION
The preservation of green plant tissue specimens is
considerably more difficult than preservation of relatively
~ibrous 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
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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 rela-tively small amount of Eibre 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 Eibres. In
succulents, mosses, ferns and lichens there is so little fibre
that complete dehydration and rigidity is almost impossible to
achieve. The dehydration process must be complete before the
1~ tissue is 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 consider-
able care is taken with the dehydration process, degradation
of the chlorophyll occurs. It is there~ore 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 earlierCanadian Patent 1,103,475 we
have found that rather than dehydrate leaves or other green
plant tissue and then preserve the dried tissues, it is pre-
ferable to effect an exchange process wherein the naturally
contained water in the tissue is exchanged with a water based
treatment solution containing sufficient chemical reagents to
bioloyically preserve and environmentally fix the green colours.
Buffers and the like may be added to modify the effects of
the primary chemicals.
Thus, it has been found that a suitable treatment
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solution for green plant tissues must contain Eour 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 referring to
"water" it is implicit that distilled water is normally
employed, in order to ensure uniformity or results and to
provide a readily controlled standard, bu-t it will be appreci-
ated that distillation is no-t 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 contain-
ing 1 ~ carbon atoms. Such alcohols, particularly ethyl
alcohol, isopropyl alcohol and tertiary butyl alcohol are
known to have considerable dehydration 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 simultaneous 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
u~ed in admixture with a milder alcohol such as l-propanol or
2-propanol. Ethyl alcohol, on the other hand may be used alone~
The preservative elements include biological preser~
vatives and ~.ixe:,~ and environmental f:ixers, such as sulph~rs:j!s
acid.
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The buffers, mordants and modifiers include citric
acid and cupric salts such as cupric acetate, cupric chloride
and cupric sulphate. Minor amounts of other chemicals have
been found useful modifiers, including such chemicals as garden
fertilizer and in particular 20-20-20 (N-P-K ratio) fertilizer.
; The amounts of each chemical required depends upon the type of
leaf being treated, the exchange medium being used and other
factors. Some chemicalsappear 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
is generally maintained in the range 6-8, i.e. substantially
neutral, pH as low as about 2 may also be employed.
The procedures to be adopted for treatment of the plant
tissue are simple and straightforward. Firstly a treating 501u-
tion is prepared by mixing the re~uired chemicals, preferably
in the order as noted below, and t:hen immersing the specimens
in 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 longer. Leaves of suc-
culents 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 with the se~ection of the exchange medium as it appears diL-
ficult to balanc~ he rate of exchange of natural water with the
treating solutiori. (-~enerally, upon immels.oll in the bath t~le co7~-
our of the leaves :ha~ges usually ~o a li~ ter green, the~ as -.he
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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 solutionl 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 after
that time. If it is desired to preserve the specimens for
later use (i.e. spring or summer leaves for use as teaching
aids in mid-winter~ or for permanent display, a secondary treat-
ment 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
temperature 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 holdi~g solution, depending on the
end use. There is, therefore, no practical limit to the treat-
ment time in the holding solution.
Treatment of ~orest mosses, lichens, sword ferns,
grasses, asparagus ferns, sphagnum mosses, oregon grape, salal
and the like present special problems because of their delicate
texture and we have found that a solution comprising:
425 ml distilled water
14.2 g cupric sulphate
56 ml propionic acid
75 rnl sulphurous acid
25 ml formic acid
10(! ml formalin
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80 g cupric chloride
10 g 20-20-20 N-P-K fertilizer
42 g citric acid
2.8 g magnesium sulphate
25 ml acetic acid
10 g cupric acetate
10 g cupric nitrate
10 g sodium phosphate (dibasic)
5.6 g sodium sulphite
238 ml 2-propanol
.21 g butylated hydroxytoluene
42 ml ethylene glycol
14 ml glycerol
is particularly suitable.
Salal may also be effectively treated in a solution
comprising:
362.5 ml distilled water
14.05 g cupric sulphate
94 ml propionic acid
80 ml sulphurous acid
40 ml formic acid
50 ml formalin
20 g cupric chloride
25 g 20-20-20 N-P-K fertilizer
65.5 g citric acid
(Dibasic ester ~ an esterified waste by-
40 ml DBE product of acrylic manufacture from Dupont
Canada Ltd.)
2.7 g magnesium sulphate
5.4 g sodium sulphite
229.5 ml 2-propanol
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.2 g butylated hydroxytoluene
40.5 ml ethylene glycol
13.5 ml glycerol.
Coniferous needles such as white spruce, balsam,
white cedar and junipers and other leaves such as ferns and
holly may be most effectively treated in a solution comprising:
362.5 ml distilled water
14.05 g cupric sulphate
104 ml propionic acid
lO100 ml sulphurous acid
50 ml formic acid
50 ml formalin
20 g cupric chloride
25 g 20-20-20 N-P-K fertilizer
; 6505 g citric acid
5.4 g sodium sulphite
229.5 ml 2-propanol :
.2 g butylated hydroxytoluene
40.5 ml ethylene glycol
20 13.5 ml glycerol.
Example
After treating selected leaves in an appropriate
solution as noted hereinabove r under the standard conditions
as also noted~ the resultant treated leaves were evaluated for
colour and texture~ The results are tabulated in Table 1
below:
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TABLE 1
Solution Solution Solution
Speclmens 1 2 3
mosses, forest excellent
c & t
__
lichens exc~llent
e & t
... ..
sword ferns very good
c & t
grasses very good
c & t
asparagus ferns very good - -
mosses, sphagnum ~ood _ - - _
Oregon grape _ good
salal poor O.K. for
_ ` _ present
arbutus poor-fair - - _
black sprueegood ~ -
white sprueegood - good
balsam poor - good
geranium fair - _
holly - - good
sugar maple
silver maple - - -
bireh - _ - _
white cedar -_ - good
greenhouse ferns = - good
junipers - - good
red oak
basswood
cat--tails
beeeh
flowering erab
elm - - - _
lareh poor - -
e = eolour
t = texture
