Abstract:
Seeds are treated in a cold plasma in a reaction chamber to etch the surface of the seeds to remove surface materials, such as fungicides and insecticides, or to disinfect the surfaces. The cold plasma process is carried out using etch gases which do not harm the seeds and for selected periods of time sufficient to remove surface materials without necessarily affecting the viability of live seeds after treatment. Tumbling the seeds while exposing the seeds to the plasma allows the surfaces of the seeds to be etched uniformly.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of provisional application No. 60/141,045, filed Jun. 24, 1999, the disclosure of which is incorporated by reference. 
    
    
     This invention was made with United States government support awarded by the following agency: NSF Grant No. 8721545. The United States government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     This invention pertains generally to the field of plasma processing of materials and particularly to plasma treatment of seeds. 
     BACKGROUND OF THE INVENTION 
     Seeds produced by commercial seed companies are commonly treated with insecticides and fungicides to enhance the survivability and germination rate of the planted seed. The fungicides and pesticides may be applied to the seed in a dry or wet form. A dry treatment involves application of the active ingredient in an inert dust which may contain additives to prevent agglomeration of the particles or “stickers” to enhance adhesion to the seed surface. Adhesion of dry particles to the seed surface is a complex process which involves molecular forces and physical trapping of small particles. Both molecular forces and physical trapping of particles are strongly dependent upon the particle size. Molecular forces of adhesion are very high per unit area and essentially depend on the surfaces that are in actual contact. Rough surfaces have low contact areas and, as a consequence, molecular forces generally play a less important role in adhesion between such surfaces. Physical entrapping of active particles is also related to the particle size. The porosity of the seed surfaces should be comparable with the average particle size to obtain efficient trapping of particles to the seed. 
     Wetting agents can also be used to allow powdery active materials to be applied to seeds using a slurry treatment. Such treatments usually are performed under low liquid volume conditions, but still have the disadvantage that the seeds generally must be dried afterwards, which increases the expense of the treatment process. 
     The result of such treatments, in whatever manner performed, is a fairly high concentration of active ingredients on the seed surfaces which, of course, enhances the utility of these seeds when planted in the normal course. However, for a variety of reasons, large quantities of treated seed either are not or cannot be used for planting within an appropriate time after the seeds have been treated. Often, seed companies treat more seeds than are expected to be used during a planting season to-ensure the availability of seeds in a subsequent season if there is an intervening crop failure. In most years, the additional seed is not planted. Over long storage times, the active ingredients in the surface treatments may degrade, leading to the formation of secondary compounds which are not active for the intended purpose of the surface treatment. However, such contaminants may present fairly high toxicity levels. Thus, such overaged treated seed is not acceptable for use as seeds for planting or for human or animal feed. Wet-chemical removal of fungicide, pesticide or insecticide contaminants from seeds would require large quantities of liquids (water, organic solvents) and expensive drying technologies. In addition, the combination of long storage times and liquid treatments may enhance the penetration of the surface borne chemicals into the seeds, potentially damaging or killing the seeds. Seeds with cracks or exposed embryos, such as from thresher damage or ventilation, may absorb even higher quantities of the surface borne toxins. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, seeds are treated by exposing the seeds to a cold plasma to etch the surface of the seeds to remove surface materials, such as fungicide and insecticide chemicals, and/or to disinfect the surface. The cold plasma etching process may be carried out employing etch gases which are not themselves harmful to the seeds, and for selected periods of time sufficient to remove surface materials such as chemicals or other contaminants without significantly affecting the viability of the live seeds.after treatment. The plasma treatment process can be carried out .under conditions allowing removal of a selected thickness of surface material from the seeds with precision. In addition, because the plasma treatment process is carried out under dry conditions, no additional moisture need be added to the seeds during the treatment process, and moisture may even be removed from the seeds during the plasma treatment. 
     A cold plasma process in accordance with the invention has several advantages over liquid-based treatment processes for detoxification of seeds or removal of surface materials from seeds. Because large quantities of liquids, such as solvents, are not needed, and only small amounts of gas-phase materials are required, the process has much less environmental impact than liquid-based processes. Because of the low pressures under which the plasma reactions develop, minimal quantities of the plasma gases are required to sustain the plasma discharge. The plasma processing conditions can be selected so that the plasma species penetrate and interact only with the very top layers of a seed, leaving the bulk of the seed unaffected. The plasma species can interact efficiently with the surface layer molecules, and regardless of the nature of such molecules, molecular fragmentation (etching) of the surfaces can take place. Various plasma process parameters, such as power coupled to the plasma, gas pressure, and treatment time, can be selected to tailor the etch rate and the nature of the gas-phase components that result after the treatment. The molecules or molecular fragments resulting from the etching process usually are gas-phase components which can easily be removed from the system. Depending on the nature of the plasma gases employed, which may be inert or reactive gases (e.g., argon, CF 4 , air, oxygen, water vapor, etc.), the etch rates and the chemical nature of the resulting volatile components (toxic or non-toxic derivatives) can also be controlled and tailored to specific process requirements. The plasma generated gas-phase components that result from the process can be easily trapped and disposed of if they constitute hazardous waste or, if non-hazardous, may be released to the environment. 
     In a preferred method of treating seeds in accordance with the invention, the seeds to be treated are enclosed in a reaction chamber, the reaction chamber is evacuated to a base level, and a selected source gas is supplied to and a selected pressure established in the reaction chamber. The gas may be provided from an external gas source and is selected to yield a desired etch characteristic and not a deposit during the processing. The gas may constitute water vapor emitted from the seeds themselves as the pressure within the reaction chamber is reduced below atmospheric. Further, multi-step processes may be carried out. For example, an initial cold plasma may be ignited in the water vapor evolved from the seeds, and the seeds may be exposed to this plasma for a selected period of time. An external gas may then be introduced into the reaction chamber and the cold plasma ignited in the external source gas. The gas in the chamber may be ignited by coupling RF power to the gas in the chamber in various ways, including capacitive coupling and inductive coupling. In addition, the RF power may be coupled in pulses to the plasma in the reaction chamber. 
     Virtually any type of seed can be treated in accordance with the present invention. The invention has particular application to seed corn which is conventionally treated with insecticides and fungicides. After treatment in accordance with the present invention to plasma etch the surface borne chemicals therefrom, the corn or other seeds may be used for animal feed, or may be retreated with insecticides, etc. at a later time so that the seeds will be properly treated for use in a later growing season. 
     Gases that may be employed in accordance with the present invention may be any of the various reactive gases which will provide plasma etching in a cold plasma process. For example, gases including, but not limited to, argon, CF 4 , air, oxygen, water vapor, and mixtures thereof may be used in the process. 
     Cold plasma treatment in accordance with the present invention may also be employed to reduce the amount of extraneous flakes and dust intermixed with the seed by physical ablation of such materials or by oxidation, thus providing a cleaner bulk seed product after treatment with less dust (possibly carrying toxic particles) than is typically the case with normal bulk seeds. 
     A cold plasma etching process in accordance with the invention may also be carried out on either treated or untreated seed, to remove all or part of the surface layers of the seed for various purposes, including affecting the germination rates of the seed by, e.g., changing the water absorption characteristics of the seed surfaces. The plasma etching process may be carried out to remove selected depths of the surface layers of the seed, including, if desired, entire removal of the pericarp. 
     Further objects, features, and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a schematic view of a plasma reactor system for carrying out the present invention. 
     FIG. 2 is a chromatogram of surface chemicals detected on corn seeds before and after plasma treatment in accordance with the invention. 
     FIG. 3 is a portion of a chromatogram as in FIG. 2 showing the peak for δ-4-tetrahydrophthalimide. 
     FIG. 4 is a portion of a chromatogram as in FIG. 2 showing the peak for Captan 50W. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention encompasses cold plasma removal of material from the surfaces of seeds. If desired, such a process can be carried out without significantly affecting the viability of the seeds. Cold plasmas are non-thermal and non-equilibrium plasmas. The plasma temperatures are near normal atmospheric temperatures and generally well below the boiling point of water. In contrast, hot plasmas are thermal or equilibrium plasmas. In a cold plasma, the kinetic energy of the electrons in the plasma is high while the kinetic energy of the atomic and molecular species is low. On the other hand, in a hot plasma, the kinetic energy of all species is high. Consequently, organic materials would be damaged or destroyed in a hot plasma. It has been discovered in accordance with the present invention that appropriate cold plasma treatment of living matter, such as seeds, not only does not destroy the seeds, but allows the seeds to remain viable so that they will germinate when planted under appropriate conditions. 
     With reference to FIG. 1, an exemplary cold plasma reactor system which may be utilized to carry out the invention is shown generally at  10 . The reactor system  10  includes a cylindrical reaction vessel  11  (e.g., formed of Pyrex® glass, 1 m long and 10 cm inside diameter) which is closed at its two ends by disk shaped stainless steel end sealing assemblies  12  and  13 . The end sealing assemblies  12  and  13  are mounted to mechanical support bearings  16  and  17  which engage the sealing assemblies  12  and  13  to enable rotation of the reaction vessel  11  about its central axis, i.e., the central axis of the cylindrical reaction vessel. Hollow shaft (e.g., 0.5 inch inside diameter) ferrofluidic feedthroughs  19  and  20  extend through the end sealing assemblies  12  and  13 , respectively, to enable the introduction of gas into and the exit of gas from the reaction chamber. A semi-cylindrical, exterior copper upper electrode  21  is connected to a power supply  22 , and a lower, similar exterior semi-cylindrical copper electrode  24  is connected to ground (illustrated at  25 ). The two electrodes  21  and  24  closely conform to the cylindrical exterior of the reaction vessel  11 , are spaced slightly therefrom, and together extend over most of the outer periphery of the reaction vessel, but are spaced from each other at their edges a sufficient distance to prevent arcing or discharge between the two electrodes  21  and  24 . The foregoing electrode arrangement is only exemplary of the many electrode arrangements that may be used to couple power to the plasma. For example, a central internal electrode (not shown) may be extended into the reaction chamber along the central axis rather than using external electrodes. 
     The present invention allows seeds to be surface etched with cold plasmas provided from a variety of source gases. The source gases may be held in containers  26 , e.g., storage tanks. The source gases in the containers  26  may be a variety of gases (e.g., argon, ammonia, air, oxygen, CF 4 , etc.) which are typically compressed under pressure. The source gas may also be provided from other sources, solid or liquid, that are appropriately volatized, and may comprise aerosols of liquid or solid particulates, such as water vapor, all of which shall be referred to herein as a “gas”. The flow of gas from a source cylinder  26  may be controlled by needle valves and pressure regulators  27  which may be manually or automatically operated. The gas that passes through the control valves  27  is conveyed along supply lines  28  through flow rate controllers  30  to a gas mixing chamber  31  (e.g., preferably of stainless steel). An MKS pressure gauge  32  (e.g., Baratron) is connected to the mixing chamber  31  to monitor the pressure thereof. A supplementary valve  33  is connected to the mixing chamber  31  to allow selective venting of the chamber as necessary. The mixing chamber  31  is connected to the feedthrough  19  that leads into the interior of the reaction vessel  11 . 
     A, e.g., digital controller  34  may be employed to control a driver motor  35  that is coupled to the reaction vessel  11  to provide controlled driving of the reaction vessel  11  in rotation. The reactor vessel  11  may be rotated by the drive motor  35  at various selected rotational speeds (e.g., 30-200 rpm). 
     The second feedthrough  20  is connected to an exhaust chamber  37 , which is coupled via selectively openable exhaust valves  38 ,  39  and  40 , to conduits for exhausting to the atmosphere or to an appropriate recovery system or other disposal route of the exhaust gases in the exhaust chamber  37 . 
     A liquid nitrogen trap  42  may be connected to an exhaust line  43  which extends from the chamber  37  by stainless steel tubing  44 . The trap  42  may be formed, e.g., of stainless steel (25 mm inside diameter). A mechanical pump  45  is connected through a large cross-section valve  46  via a tube  47  to the trap  42  to selectively provide a vacuum draw on the reactor system  10  to evacuate the interior of the reaction vessel  11  to a selected level. It is preferred that the vacuum pump and associated connections allow the pressure in the reaction chamber within the vessel to be selectively reduced down to 30 mT. 
     The power supply  12  is preferably an RF power supply (e.g., 13.56 MHz, 1,000 W) which, when activated, provides RF power between the electrodes  21  and  24  to capacitively couple RF power to the gas in the reaction chamber within the reaction vessel  11 . Conventional coils for inductively coupling RF power to the plasma may also be used (e.g., a coil extending around the reaction vessel  11 ). A Farraday cage  50  is preferably mounted around the exterior of the reaction vessel to provide RF shielding and to prevent accidental physical contact with the electrodes. 
     The reactor vessel may be rotated by the drive motor  35  at various selected rotational speeds (e.g., 30-200 rpm), and it is preferred that the vacuum pump and associated connections allow the pressure in the reaction chamber within the vessel to be selectively reduced down to 30 mT. 
     The following are examples of commercial parts that may be incorporated in the system  10 : RF-power supply  22  (Plasma Therm Inc., RTE 73, Kresson, N.J. 08053; AMNS-3000 E; AMNPS-1); mechanical vacuum pump  45  (Leibold-Heraeus/Vacuum Prod. Inc., Model: D30AC, Spectra Vac Inc.); pressure gauge  32  (MKS Baratron, Model: 622AO1TAE); digitally controlled rotating system  34 ,  35  (DC motor, Model 4Z528, Dayton Electric Mfg. Co.; DART Controls Inc. controller). 
     In utilizing the plasma treatment system  10  in accordance with the invention, it is generally preferred that a plasma-enhanced cleaning of the reactor be conducted prior to treatment to eliminate possible contaminants. An exemplary cleaning step includes introduction of oxygen gas from one of the tanks  26  into the reaction chamber and ignition of a plasma in the gas at, e.g., a power level of 300 W, a gas pressure of 250 mT, an oxygen flow rate of 6 sccm, and a typical cleaning period of 15 minutes. 
     For carrying out treatment of seeds in accordance with the invention, the reactor is opened to allow access to the interior of the reaction vessel  11  by disconnecting one of the vacuum sealing assemblies  19  or  20  from the cylindrical reaction vessel, and inserting the seeds into the interior of the vessel, followed by resealing of the assemblies into vacuum tight engagement with the reaction vessel  11 . Sealable ports may also be provided in the sealing assemblies. The pump  45  is then operated to evacuate the plasma reactor to a desired base pressure level based on the seed origin water vapor or the artificially supplied plasma gases and vapors. The desired gas is then introduced from the source containers  26 , and a desired gas pressure level in the reaction chamber is established. The RF power supply  22  is then turned on (generally, it is preferred that the power be supplied in pulses) to ignite the plasma in the gas introduced into the reaction chamber defined by the reaction vessel  11  and the end sealing assemblies  12  and  13 . For treating seeds, it is preferred that the drive motor  35  be operated to rotate the reaction chamber  11  to tumble the seeds during the plasma reaction process so that all surfaces of the seeds are exposed to the plasma for a relatively uniform period of time to enable the surfaces of the seeds to be uniformly etched. Because the seeds are exposed to a dry gas during plasma treatment, no additional moisture need be introduced into the seeds, and because of the evacuation of the chamber below atmospheric pressure, some removal of moisture from the seeds during plasma processing can be obtained if desired. After a period of time selected to sufficiently remove a selected material from the surface of the seeds has elapsed, the power supply  22  is turned off. The pump  45  is then operated to evacuate the reaction chamber to draw out the remaining source gases and any byproducts. These can be vented to the atmosphere or disposed of as appropriate. Atmospheric air, or another selected gas, is then introduced into the chamber to bring the pressure in the reaction chamber to normal atmospheric pressure. One of the sealing assemblies  12  or  13  is then opened to allow removal of the treated seeds. 
     If desired, the plasma treatment processes can be periodically stopped to allow samples of the seeds to be collected for analytical and biological evaluations. 
     In addition to the preferred RF plasma reaction apparatus discussed above, the invention may be carried out using other plasma treatment apparatus, including static inductively or capacitively coupled RF plasma reactors, DC-discharge reactors, and atmospheric pressure barrier discharges. Such apparatus are not preferred for certain applications of the invention. Static reactors may yield non-uniform treatment of the seeds or other material. Atmospheric pressure discharges usually require a narrow electrode gap, and they generally cannot uniformly expose the seed (or other particulate matter) surfaces to the discharge. Additionally, because of the particulate nature of seeds, etc., the ability to use vacuum tight seals is limited, which may result in contamination problems. Barrier discharge processes are also less efficient because of the short free path of the plasma particles and, consequently, the fast recombination of the active species in the gas phase. 
     The active species of the plasma, including charged and neutrals species, have energies comparable with the chemical bonds of organic compounds, and consequently these species can cleave molecules and accordingly can generate active molecular fragments, such as: atoms, free radicals, ions of either polarity, etc. These molecular fragments, assisted by electrons and photons, generate specific gas phase and surface recombination reaction mechanisms which can lead to the formation of new molecular or macromolecular structures, and to the extraction of low molecular weight, volatile molecular fragments of substrate origin. 
     By controlling the external (power, pressure, flow rate, etc.) and internal (energy distribution of charged and neutral species, particle densities, etc.) plasma parameters these processes can be tailored for purposes of the present invention for predominant fragmentation processes to etch surface material from the seeds. 
     Other factors like molecular structures, gas composition, and pulsing characteristics also can influence significantly the nature of the plasma-mediated reaction mechanisms. Carbon tetrafluoride plasmas do not deposit fluorinated macromolecular layers under common RF-cold-plasma conditions due to the intense etching effects related to the high plasma-generated fluorine atomic concentrations. However, the presence in the gas mixture of fluorine atom scavengers (e.g., hydrogen) allow the deposition of macromolecular layers. There are species which, due to their molecular structures, never can deposit macromolecular layers, like oxygen, chlorine, ammonia, nitrogen, etc. In the present invention, the source gas (including mixtures) are utilized under process conditions that result in surface etching rather than surface deposit. 
     As an example of the cold plasma removal of surface material from seeds in accordance with the invention, plasma cleaning of corn treated with Captan 50 W, a commercially available brand of agricultural fungicide, was performed in the plasma reaction apparatus  10  as described above. The seeds were treated in a two-step process. The first step used a plasma generated from water vapor emitted from the seeds. The second step utilized an oxygen gas from an external source in which the plasma was ignited. During this surface cleaning process, the following conditions were utilized: RF power of 20 W; pressure in the plasma reactor of 600 mT; temperature in the reactor of 25° C.; oxygen flow rate of 2 sccm; and treatment times of 15 or 30 minutes for the water vapor plasma and 15 minutes for the oxygen plasma. 
     At the end of the plasma cleaning step, the corn seeds were removed from the reactor and stored in unsealed polyethylene bags until analytical work was carried out on the corn. Captan-treated corn control samples and the Captan-treated and plasma-cleaned corn samples were alcohol (ethanol) extracted, and the contents of the solution were analyzed by gas chromatography-mass spectroscopy (GC-MS), to allow the Captan concentrations from the seed surfaces of the samples to be evaluated. The untreated and treated seeds (10 pieces of corn per each sample) were extracted for 10 minutes with 10 mL ethyl alcohol. One μL of solution was injected into a Hewlett-Packard GC-6890+/MSD 5973 system for gas chromatographic (GC) separation and mass spectrographic identification of chemical products. The data obtained from the chromatographic analyses are summarized in Table 1 below. 
     
       
         
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                 δ-4-Tetrahydro- 
                   
               
               
                   
                 Captan 50 W(C) 
                 phthalimide (T) 
               
               
                   
                 15.716 min peak 
                 9.379 min peak 
               
               
                   
                 (FIG. 4) 
                 (FIG. 3) 
                 Ratio 
               
             
          
           
               
                 # 
                 Sample 
                 Area 
                 % 
                 Area 
                 % 
                 T/C 
               
               
                   
               
             
          
           
               
                 1 
                 Untreated 
                 125868667 
                 100.0 
                 6869970 
                 100.0 
                 0.0546 
               
               
                 2 
                 15 min plasma 
                  27461035 
                 21.8 
                 2082733 
                 30.3 
                 0.0758 
               
               
                   
                 treated 
               
               
                 3 
                 15 + 15 min 
                  20050862 
                 15.9 
                 1560815 
                 22.7 
                 0.0784 
               
               
                   
                 plasma treated 
               
               
                 4 
                 15 + 15 min 
                  5213547 
                 4.1 
                  525812 
                 7.6 
                 0.1008 
               
               
                   
                 plasma treated 
               
               
                   
                 and 15 min O 2   
               
               
                   
                 plasma treated 
               
               
                   
               
             
          
         
       
     
     FIG. 2 is a chromatogram obtained from the samples for: untreated (control) corn; 15 minutes of water vapor plasma treatment; 15 minutes of water vapor followed by 15 minutes of additional water vapor plasma treatment; and 30 minutes of water vapor plasma treatment followed by 15 minutes of oxygen plasma treatment. FIG. 3 is a portion of the same chromatogram on an enlarged scale illustrating the δ-4-tetrahydrophthalimide peak at  60  for the untreated corn; at  61  for the 15 minute water vapor plasma treatment corn; at  62  for the 15 minute water vapor followed by an additional 15 minute water vapor plasma treatment; and at  63  for the foregoing plasma treatment plus an additional 15 minutes of oxygen plasma treatment. FIG. 4 is a portion of the same chromatogram of FIG. 2 at an enlarged scale showing the Captan peak for the untreated corn at  65 ; for the 15 minute treated corn at  66 ; for the 15 minute water vapor treatment followed by 15 minute water vapor plasma treatment at  67 ; and for the foregoing treatment followed by an additional 15 minutes oxygen plasma treatment at  68 . The results of these experiments show the Captan level of the plasma treated corn can be reduced to very low levels. 
     Seeds which were treated to remove the Captan from the surfaces of the seeds were then subjected to germination tests to determine the effect of the plasma treatment on germination. Germination tests were performed on Captan treated seeds having normal one-year carryover; on seeds from the same batch which were plasma treated in accordance with the present invention to remove the Captan service material; and on seeds that had been plasma treated and which were then retreated with Captan. 
     The percent germination, range of germination for the samples, and the range difference for the three types of samples under warm germination and cold germination conditions are shown in Table 2 below. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
                   
                 Planted 5/24/99 
                   
                 Read 6/3/99 
                   
               
               
                 Normal 
                   
                 Detreated 
                   
                 Retreated 
               
             
          
           
               
                 Normal 
                 Normal 
                 Normal 
                 Normal 
                 Normal 
                 Normal 
               
               
                 1 year 
                 1 year 
                 1 year 
                 1 year 
                 1 year 
                 1 year 
               
               
                 Carry- 
                 Carry- 
                 Carry- 
                 Carry- 
                 Carry- 
                 Carry- 
               
               
                 over 
                 over 
                 over 
                 over 
                 over 
                 over 
               
               
                 Seed 
                 Seed 
                 Seed 
                 Seed 
                 Seed 
                 Seed 
               
               
                 Warm 
                 Cold 
                 Warm 
                 Cold 
                 Warm 
                 Cold 
               
               
                 Germi- 
                 Germi- 
                 Germi- 
                 Germi- 
                 Germi- 
                 Germi- 
               
               
                 nation 
                 nation 
                 nation 
                 nation 
                 nation 
                 nation 
               
               
                   
               
               
                 94 
                 93 
                 87 
                 54 
                 85 
                 57 
               
               
                 Range 
                 Range 
                 Range 
                 Range 
                 Range 
                 Range 
               
               
                 92-98 
                 92-96 
                 84-96 
                 46-60 
                 84-90 
                 54-60 
               
               
                 Range 
                 Range 
                 Range 
                 Range 
                 Range 
                 Range 
               
               
                 Differ- 
                 Differ- 
                 Differ- 
                 Differ- 
                 Differ- 
                 Differ- 
               
               
                 ence 
                 ence 
                 ence 
                 ence 
                 ence 
                 ence 
               
               
                  6 
                  4 
                 12 
                 14 
                  6 
                  6 
               
               
                   
               
             
          
         
       
     
     For comparison purposes, similar germination tests were performed on seeds that were not Captan treated to compare the germination rates of the non-treated (natural surface) seeds and the germination rates of the same seeds after a plasma surface removal treatment as in the example above. The results of these tests showing the percent of warm and cold germination, the range of germination, and the range differences are given in Table 3 below. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 No Plasma Treatment 
                   
                 Plasma Treated 
                   
               
             
          
           
               
                   
                 Regular 
                 Regular 
                 Regular 
                 Regular 
               
               
                   
                 non treated 
                 non treated 
                 non treated 
                 non treated 
               
               
                   
                 Seed 
                 Seed 
                 Seed 
                 Seed 
               
               
                   
                 Warm 
                 Cold 
                 Warm 
                 Cold 
               
               
                   
                 Germination 
                 Germination 
                 Germination 
                 Germination 
               
               
                   
                   
               
               
                   
                 97 
                 81 
                 95 
                 72 
               
               
                   
                 Range 
                 Range 
                 Range 
                 Range 
               
               
                   
                 96-98 
                 72-92 
                 88-98 
                 64-78 
               
               
                   
                 Range 
                 Range 
                 Range 
                 Range 
               
               
                   
                 Difference 
                 Difference 
                 Difference 
                 Difference 
               
               
                   
                  2 
                 20 
                 10 
                 14 
               
               
                   
                   
               
             
          
         
       
     
     It is understood that the invention is not confined to the particular embodiments set forth herein as illustrative, but embraces such modified forms thereof as come within the scope of the following claims.