as the present inventors have noted before , bleeding of treatment chemicals is a serious problem after high humidity exposure of conventionally treated preserved plants . in those preserved plants which have been of sufficiently high quality for successful commercial sale , glycerine has almost universally been the preservative material employed . many species of preserved plant materials are now available for decorative uses . these range from small trees up to about 7 meters in height down to smaller plants which are used in floral arrangements . of the tree sized plants , palms are of particular commercial significance with two species having primary importance . these are pheonix canariensis , the canary island date palm and washingtonia robusta , a representative of the fan palms . in addition to the problem of bleeding , a second problem has arisen with these species . the normal treatment with glycerine gives a relatively limp stem or petiole so that over time the leaves tend to droop and ultimately become fixed in drooped position . a second problem is that the leaves of the glycerine teated fan palms frequently do not open to their broadest extent . these conditions are represented in fig1 and 3 which are ink drawings make from actual photographs . quite surprisingly the above problem of leaf droop has been solved using any of the humectant preservative materials of the present invention . fig2 and 4 shown washingtonia palm treated using tripropylene glycol as the preservative material . note in fig2 . that the fan has remained open to its widest extent and in fig4 that the petioles remain straight and the leaves or fans are in their normal position . this advantage was entirely unexpected and the reasons for it are not fully understood . the following examples will teach the best most presently known to the inventors of practicing the method of their invention . ______________________________________humectant 30 . 00 % by weightwater 69 . 28potassium nitrate 0 . 555citric acid 0 . 0083c . i . acid red no . 52 * 0 . 152biocide trace______________________________________ * c . i . no . 45100 this red treatment solution was chosen for test purposes since untreated portions of the plants are more readily apparent than is the case with the more usual blue - green dyes . plants to be treated were severed from the roots and the cut ends placed in the solution for 3 - 14 days , at a solution and environment temperature of 20 °- 45 ° c . and a relative humidity normally 60 % or under . however , deviations from all of these conditions were occasionally made , as will be noted in the following examples . where humectant concentration was varied above or below 30 % an equivalent amount of water was removed or added to keep the combined amount of humectant plus water constant . treatment conditions were adjusted depending on the species and variety of plant and the growth stage or season in which it was treated . there is great variation both within and between species and no single set of conditions or composition of treating solution is always ideal for any given variety . treatment conditions must usually be adjusted based on past experience and trial runs . some plant species do not respond at all satisfactorily to preservative treatments . others may respond well at some seasons and not at others . in general , the best quality is achieved when the plant being treated is in a season of active growth . following treatment with the perservative solution the plants were normally conditioned for 2 - 3 days at 20 °- 22 ° c . and about 50 - 65 % r . h . before further evaluation . the quality of treated plants is ranked on an arbitrary scale of 1 - 5 based on appearance and ultimate marketability . this scale is as follows : ______________________________________rating description salable______________________________________5 well treated , good color and uniformity yes4 well treated , slight nonuniformity yes3 most1y treated , mottled , slightly dry questionable2 dye in and adjacent to midveins only , no foliage mostly dry1 untreated , dry foliage no______________________________________ by well treated is meant that the treatment solution has been taken up uniformly to the edges and tips of the foliage , as indicated by dye distribution , and the foliage is generally soft , supple , and of natural feel and appearance , except perhaps for color . conditioned plants were then tested for bleed resistance by placing them in an environmental chamber at 90 % r . h . and 21 ° c . for 14 days . samples were checked daily for visible bleeding at several sites . these included young or immature stems , mature stems , leaves , flowers and any cut or abraded stem areas . almost invariably bleeding would first occur at cut or abraded areas then , most usually , from young or immature stem portions of the plants . the following plant species were the subject of preservation tests : eucalyptus gunnii , gypsophilia paniculata ( baby &# 39 ; s breath ), limonium sinuata ( statice ), fagus sylvatica ( european beech ), juniperis chinensis cv . bluepoint , mahonia aquifolium ( oregon grape ), gaultherica shallon ( salal ), pheonix canaeriensis ( canary island date palm ), and washingtonia robusta ( fan palm ). hereafter these plants are generally referred to only by genus ; i . e ., &# 34 ; limonium &# 34 ; should be considered to always mean limonium sinuata . all of these plants are commercially important species in the preserved ornamental plant trade . as noted earlier , the principal function of a preservative / humectant is to replace , at least in part , the water normally present in the plant tissues with a material of low volatility . this preservative must also be at least somewhat hygroscopic to prevent dry out at low humidity with resulting curling and poor appearance , especially of the leaves of broadleaf species . glycerine has been used almost universally in the past as the preservative material of commercial interest . its effectiveness has been so well known there has been little effort or incentive to look for other materials that might serve as well or better . the present inventors have determined that bleeding at high humidities is caused by the hygroscopic nature of the humectant / preservative material . it is a characteristic of hygroscopic materials that they continue over time to take up moisture and asymptotically approach some limiting amount . this amount is dependent on the material itself and the temperature and relative humidity of the ambient environment . thus , rate and amount of water pickup is relatively high initially but continually decreases over time . bleeding will not occur as long as there is some unfilled void volume remaining in the treated plant . if , however , the void spaces become filled with liquid , water pickup still continues . there is no place within the plant structure to accommodate this extra volume of liquid and bleeding occurs through leaf stomata or other available openings . the present inventors have investigated a large number of potential compounds for their stability as ( 1 ) preservative / humectants and ( 2 ) the contribution they make to the bleeding problem . a first screening test was to expose open dishes of each material to a 90 % r . h ., 21 ° c . atmosphere for extended periods of time . weight gain was measured periodically during the test period . materials tested and the weight gain results are shown in table i . table i______________________________________ % weight gain at 21 ° c . and 90 % r . h . after various times , hourssample material 7 24 48 72 144 204 408______________________________________glycerol 10 26 41 53 80 102 129polyethylene glycol 200 10 24 38 47 68 84 102polyethylene glycol 400 12 24 32 39 54 67 82polyethylene glycol 600 * 9 19 28 36 52 67 83polyethylene glycol 1000 * 5 13 22 29 46 60 75polyethylene glycol 3250 2 4 6 7 9 13 23dipropylene glycol 13 27 37 43 56 69 85tripropylene glycol * 12 23 30 35 44 52 631 , 3 - butanediol 15 31 42 49 66 81 10195 % tpg - 5 % glycerol 11 22 31 37 50 62 8230 % tpg - 70 % glycerol 12 25 35 43 57 69 8770 % peg 600 - 30 % glycerol 10 23 35 44 65 80 9750 % peg 600 - 50 % glycerol 10 23 36 45 66 83 10370 % peg 1000 - 30 % glycerol 7 18 29 37 56 71 8850 % peg 1000 - 50 % glycerol 7 18 33 45 -- 91 11150 % tpg - 50 peg 600 11 24 35 43 57 69 85______________________________________ * results for peg 600 and 1000 are averages from three trials . those for tpg are averages from two trials . of all the materials tested , glycerol showed the highest weight gain over time . mixtures of glycerol with less hygroscopic compounds showed intermediate results roughly proportional to the percentages of the individual components . to demonstrate the bleeding propensity of a glycerine based preservative , five species were treated using varying conditions designed to give a wide range of ultimate glycerine uptake . preservative uptake is based on grams of preservative per 100 g of fresh plant weight . this is calculated from the measured solution uptake multiplied by solution density and concentration of humectant / preservative in the solution . where a concentration other than 30 % glycerine ( or other humectant ) was used , an appropriate adjustment was made by increasing or decreasing the amount of water in treating solution . table ii__________________________________________________________________________glycerine - based preservativessample preservative treatment conditions uptake quality bleed timeno . species conc ., % time , hr . temp ., ° c . r . h ., % g / 100 g rating days__________________________________________________________________________1 eucalyptus 30 261 21 65 47 5 12 eucalyptus 20 261 21 65 37 5 13 eucalyptus 10 260 21 65 51 5 14 eucalyptus 5 260 21 65 21 5 15 eucalyptus 2 260 21 65 10 5 56 gypsophilia 50 65 40 60 40 5 1 * 7 gypsophilia 40 65 40 60 41 5 1 * 8 gypsophilia 30 65 40 60 40 5 1 * 9 gypsophilia 20 65 40 60 35 5 1 * 10 gypsophilia 10 65 40 60 25 5 1 * 11 phoenix 30 213 21 60 20 3 - 4 1 - 512 fagus 30 214 21 60 29 5 113 juniperis 30 214 21 60 25 4 - 5 3__________________________________________________________________________ * severe bleeding only in the case of sample no . 5 , where glycerine takeup was very low , did bleed resistance exceed four days . four days is considered to be a desirable minimum time for freedom from bleeding . this corresponds to the time an office building might be without air conditioning over a long holiday weekend . humidity and / or temperature could rise to values well above normal under such conditions . the first group of new materials to be tested as potential low bleeding preservatives , from those screened in example 2 , were polyethylene glycols ( peg ) having a range of average molecular weights . these materials have the formula h ( och 2 ch 2 ) m oh where m is 2 - 35 . among the materials tested the following relationship exists : ______________________________________average m . w . m ( approximately ) ______________________________________ 200 4 400 9 600 131000 221450 32 . 52000 453250 73 . 5______________________________________ test results using perservation treatment solutions , all having 30 % peg , are given in table iii . table iii__________________________________________________________________________polyethylene glycol - based preservativessample preservative treatment conditions uptake quality bleed timeno . species material conc ., % time , hr . temp ., ° c . r . h ., % g / 100 g rating days__________________________________________________________________________14 eucalyptus peg 200 30 215 21 65 -- & lt ; 5 4 - 515 eucalyptus peg 400 30 215 21 65 -- & lt ; 5 & gt ; 1416 eucalyptus peg 600 30 215 21 65 -- & lt ; 5 & gt ; 1417 eucalyptus peg 1000 30 215 21 65 -- 3 - 4 & gt ; 1418 eucalyptus peg 1450 30 215 21 65 -- 4 3 - 819 eucalyptus peg 2000 30 215 21 65 -- 3 & gt ; 1420 eucalyptus peg 3250 30 215 21 65 -- 2 & gt ; 1421 limonium peg 400 30 91 40 60 21 5 122 washingtonia peg 200 30 -- 40 60 35 5 1 - 423 gypsophilia peg 400 30 65 40 60 21 3 & lt ; 1__________________________________________________________________________ bleed results improve ; i . e ., bleeding tendency decreases , with increasing average molecular weight of the peg . conversely , quality appears to be poorer as molecular weight increases . satisfactory quality was not obtained with peg having a molecular weight greater than about 1450 . apparently the larger aliphatic dihydroxy polyether molecules are too large to effectively diffuse uniformly through the plant tissue . the three species represented by sample nos . 21 - 23 did not have good bleed resistance under the conditions used . this points up what was noted before . not all preservation treatments will work well for all species at all times during the seasonal periods . blends of various peg materials were made with glycerine . in no case did the amount of glycerine exceed more than 1 / 6 of the active perservative / humectant materials . treating solution compositions , conditions , and results are given in table iv . the preferred polyethylene glycol oligomers have from 2 - 35 [ och 2 ch 2 ] units , corresponding to average molecular weights in the range of about 100 - 1600 . the most preferred materials are in the average molecular weight range of 400 - 1200 . table iv__________________________________________________________________________polyethylene glycol / glycerine - based preservativessample peg glycerine treatment conditions quality bleed timeno . species type % % time , hr . temp ., ° c . r . h ., % rating days__________________________________________________________________________24 eucalyptus 600 25 5 215 21 65 4 3 - 725 eucalyptus 1000 25 5 215 21 65 4 3 - 426 eucalyptus 1450 25 5 215 21 65 4 3 - 1327 eucalyptus 2000 25 5 214 21 65 3 & gt ; 1428 eucalyptus 3250 25 5 214 21 65 2 & gt ; 1429 eucalyptus 1000 25 5 214 21 65 4 5 - 630 eucalyptus 1000 26 4 214 21 65 4 6 - 831 eucalyptus 1000 27 3 214 21 65 4 - 5 4 - 932 eucalyptus 1000 28 2 214 21 65 4 7 - 833 eucalyptus 1000 29 1 214 21 65 4 2 - 734 eucalyptus 1000 30 0 214 21 65 4 2 - 9__________________________________________________________________________ in general , satisfactory quality and fair to excellent bleed resistance was obtained in all samples tested , with the exception of nos . 27 and 28 . these two samples were made using peg having molecular weights above the desired range . it is believed that ethylene or propylene glycol could be substituted in whole or part for glycerine . tripropylene glycol ( tpg ) has been found to be an excellent preservative material , combining the attributes of good product quality with generally excellent bleed resistance . tests were run using five plant species with various tpg concentrations and treatment conditions . these conditions and the results obtained are given in table v . table v__________________________________________________________________________di - and tripropylene glycol - based preservativessample preservative treatment conditions uptake quality bleed timeno . species conc ., % time , hr . temp ., ° c . r . h ., % g / 100 g rating days__________________________________________________________________________35 eucalyptus 20 259 21 65 23 3 - 4 336 eucalyptus 10 259 21 65 20 4 237 juniperis 30 259 21 65 21 4 & gt ; 1438 juniperis 50 66 40 60 26 5 1 - 739 juniperis 40 66 40 60 22 5 740 juniperis 30 66 40 60 18 5 741 juniperis 20 66 40 60 12 5 & gt ; 1442 juniperis 10 66 40 60 8 5 & gt ; 1443 gypsophilia 30 65 40 60 19 4 244 gypsophilia 20 65 40 60 17 5 245 gypsophilia 10 65 40 60 11 5 246 phoenix 30 68 40 60 20 5 1347 phoenix 20 68 40 60 14 5 & gt ; 1448 mahonia 20 143 30 60 14 4 & gt ; 1449 mahonia 10 143 30 60 9 4 & gt ; 1450 eucalyptus 30 * 215 21 65 -- 3 & gt ; 14__________________________________________________________________________ * dipropylene glycol substituted for tripropylene glycol . interestingly , as seen here and in the other examples , even low concentrations of preservative / humectant in the treating solution and the plant itself can give excellent product quality . the bleed resistance is frequently improved as well as is seen here in sample nos . 41 and 42 . it can be stated as a generalization that the minimum amount of material necessary for good perservation should be used where bleed resistance is of concern . again , this relates to maximizing the void volume in the plant tissue available for holding moisture taken from the air during high humidity conditions . it might be noted that the gypsophilia is a species particularly prone to bleeding under even the best known treatment conditions . the two days to bleeding in sample nos . 43 - 45 should be compared with the severe bleeding in less than one day ( sample nos . 6 - 10 ) using glycerine treatment . the present results , while not as good as desired , represent a very significant improvement . dipropylene glycol , used on only sample no . 50 , gave excellent bleed resistance but only fair quality . this material would be expected to perform in generally equivalent fashion to tpg when used with other species . the molecular weight range of propylene oligomers that will give satisfactory quality appears to be narrower than for ethylene oxide oligomers . the general formula for these compounds is h ( ochch 3 ch 2 ) n oh where n is 2 - 8 . this corresponds to average molecular weights in the range of about 130 - 500 . two butanediols have been used as preservative materials with generally very good to excellent quality and good resistance to bleeding . 1 , 3 - and 1 , 4 - butandiol appear to be about equivalent to each other . conditions of treatment and results are seen in tables vi and vii . table vi__________________________________________________________________________1 , 3 - butanediol - based preservativessample preservative treatment conditions uptake quality bleed timeno . species conc ., % time , hr . temp ., ° c . r . h ., % g / 100 g rating days__________________________________________________________________________51 mahonia 50 65 40 60 24 4 252 mahonia 40 65 40 60 23 4 253 mahonia 30 65 40 60 18 5 254 mahonia 20 65 40 60 15 5 & gt ; 1455 mahonia 10 30 40 60 12 5 & gt ; 1456 gypsophilia 30 65 40 60 14 4 257 gypsophilia 20 65 40 60 14 4 158 gypsophilia 10 65 40 60 9 4 4 -& gt ; 1459 limonium 30 65 40 60 17 5 260 limonium 20 65 40 60 14 5 7 -& gt ; 1461 limonium 10 65 40 60 9 5 & gt ; 1462 gaultheria 30 65 40 60 13 2 & gt ; 1463 gaultheria 20 65 40 60 11 3 & gt ; 1464 gaultheria 10 65 40 60 10 5 & gt ; 1465 washingtonia 30 -- 40 60 34 5 & gt ; 14__________________________________________________________________________ table vii__________________________________________________________________________1 , 4 - butanediol - based preservativessample preservative treatment conditions uptake quality bleed timeno . species conc ., % time , hr . temp ., ° c . r . h ., % g / 100 g rating days__________________________________________________________________________66 mahonia 50 142 30 60 23 3 167 mahonia 40 142 30 60 23 4 168 mahonia 30 142 30 60 21 5 169 mahonia 20 142 30 60 18 5 170 mahonia 10 142 30 60 12 5 171 gaultheria 50 142 30 60 20 2 & gt ; 1472 gaultheria 40 142 30 60 17 2 & gt ; 1473 gaultheria 30 141 30 60 -- 2 . 5 & gt ; 1474 gaultheria 20 142 30 60 17 3 & gt ; 1475 gaultheria 10 141 30 60 -- 5 & gt ; 14__________________________________________________________________________ once again , the ue of low concentratons of humectant / preservative in the treating solutions result in plants showing good quality with superior bleed resistance . this is especially evident in sample nos . 54 , 55 , 58 , 60 and 61 treated with 1 , 3 - butanediol . note sample nos . 64 , 68 - 70 and 75 where product quality was also improved by the use of lower concentrations . in u . s . patent application , ser . no . 113 , 312 , filed oct . 28 , 1987 , and commonly owned by the present assignee , a number of materials are disclosed that contribute flame retardancy to preserved plants . these flame retardant materials are generally used in combination with glycerine but two groups of them serve as effective preservatives in their own right . these are water soluble cyclic phosphonate esters and magnesium chloride and bromide hexahydrate . surprisingly , the phosphonate esters especially also confer reduced bleeding used either by themselves or as a minor ingredient in combination with the polyols just described . the water soluble phosphonate esters are generally prepared by reacting alkyl - halogen free esters with a bicyclic phosphite . examples of suitable materials are as follows : ## str1 ## where a is 0 , 1 , or 2 , b is 0 , 1 , or 2 , c is 1 , 2 , or 3 and a + b + c is 3 ; r and r 1 are alkyl , alkoxy , aryl , aryloxy , alkaryl , alkaryloxy , aralkyl , aryloxy - alkoxy , or aralkoxy wherein the alkyl portion of these groups may contain hydroxyl but not halogen and the aryl portion may contain chlorine , bromine and hydroxyl groups ; r 2 is alkyl , hydroxy - alkyl , or aryl ; r 3 is lower alkyl ( c 1 - c 4 ) or hydroxyalkyl ( c 1 - c 4 ); ## str2 ## where d is 0 , 1 , or 2 ; e is 1 , 2 , or 3 ; d + e is 3 ; r 2 is as defined above , r 3 is as defined above , r 4 is alkyl , aryl , alkaryl , aralkyl , or aryloxyalkyl , wherein the aryl portion may contain bromine , chlorine or hydroxyl ; and r 5 is monovalent , divalent or tervalent alkyl , alkylene , aryl , or arylene radical wherein the aryl or arylene radical may contain bromine , chlorine , alkyl or hydroxy groups ; and ## str3 ## where r 2 and r 3 are as defined above ; and r 6 is alkyl , aryl , alkylaryl , or arylakyl wherein the aryl portion may contain bromine , chlorine or hydroxyl . preparation of these materials is described in anderson et al , u . s . pat . no . 3 , 789 , 091 . a preferred material is defined by formula a wherein a is 1 , bis 0 or 1 , and c is 2 - b ; r , r 1 , and r 3 are methyl and r 2 is ethyl . this is shown by the formula . ## str4 ## where x is 0 or 1 . the preferred composition is available as antiblaze 19 or antiblaze 19t from albright and wilson , inc ., richmond , va . antiblaze is a registered trademark of the above supplier . mixtures of tripropylene glycol and magnesium chloride hexahydrate were made for a preservation solution . the mgcl 2 . 6h 2 o was present as either 25 % or 33 % of the active preservative / humectant material . six plant speices were treated is outlined in table viii . table viii__________________________________________________________________________tripropylene glycol / magnesium chloride - based preservativessample preservative conc ., % treatment conditions uptake quality bleed timeno . species tpg mgcl . sub . 2 . 6h . sub . 2 o time , hr . temp ., ° c . r . h ., % g / 100 g rating days__________________________________________________________________________76 phoenix 30 10 259 21 65 18 5 5 -& gt ; 1477 fagus 30 10 259 21 65 19 3 & gt ; 1478 juniperis 30 10 259 21 65 16 4 579 eucalyptus 30 10 259 33 65 32 3 1 - 780 phoenix 20 10 188 24 60 16 3 & gt ; 881 phoenix 20 10 189 30 60 21 4 782 phoenix 20 10 189 40 60 28 5 283 limonium 30 10 117 24 60 14 3 384 washingtonia 30 * 10 -- 40 60 31 5 1 - 3__________________________________________________________________________ * 1 , 3 butanediol substituted for tripropylene glycol . quality and bleed resistance could generally be characterized as fair to excellent . as has been observed before , the quality of some species was superior to others treated in exactly the same manner . the inventors have herein been disclosed the best mode or modes known to them of practicing their invention . they wish to emphasize again the great variability that is to be found and expected when dealing with natural materials as diverse as living plants . any particular set of treatment conditions or materials will not be optimum for all species , nor even for any given species , at different times of the growing season . since many features of the invention other than those disclosed above will be apparent to those skilled in the art , the invention is to be considered limited only as it is defined by the following claims .
the present invention is a method of preserving plants which achieves reduced bleeding of the preservative material when the plants are subjected to elevated humidity conditions . the method comprises perfusing the plants with an aqueous preservative composition in which the preservative is primarily an alkylene oxide oligomer , 1 , 3 - butanediol , or 1 , 4 - butanediol . preferred alkylene oxide oligomers are di - and polyethylene glycols in the molecular weight range of about 200 - 1500 and di - and polypropylene glycols with an average molecular weight below about 450 . the preferred materials may be used with lesser amounts of secondary humectant materials selected from glycerol , ethylene glycol , propylene glycol , magnesium chloride or magnesium bromide hexahydrate , and water soluble cycle phosphonate esters . plants are conventionally treated by perfusing an aqeous treatment solution into the vascular system through a cut stem or other incision which exposes the xylem . treatment is carried out at a temperature in the range of 20 °- 50 ° c . at a relative humidity in the range of about 20 %- 80 % for a period time up to about 14 days .