WO1988004520A1

WO1988004520A1 - Apparatus for and methods of cutting and/or moving plant tissue

Info

Publication number: WO1988004520A1
Application number: PCT/GB1987/000918
Authority: WO
Inventors: Frank Raymond Brown
Original assignee: Twyford Plant Laboratories Limited
Priority date: 1986-12-22
Filing date: 1987-12-22
Publication date: 1988-06-30
Also published as: AU1080088A; GB8630610D0

Abstract

A cutting device for cutting plant shoots for micropropagation has a cutter (20) with a circular cutting edge (21). The cutter (20) is pressed against the plant tissue by a barrel shaped handle (18) and the cut is effected by rotating the barrel (18). The plant cutting is transferred by being lodged in a recess (22) inside the cylindrical cutter (20), and is expelled at a required position by depressing a push-button (24) to move a shaft and collar (23 and 25) downwardly within the cylindrical cutter (20) to push out the cutting. The cutting is oriented on the surface of a soft nutrient medium by a tool (31) having a shaft (33) and lateral projection (34). The projection (34) is placed across the stem portion of the cutting and is pressed down so as to tip the plant cutting upright with one end in the medium.

Description

APPARATUS FOR AND METHODS OF CUTTING AND/OR MOVING PLANT TISSDE

The present invention relates to apparatus for and methods of cutting and/or moving plant tissue, e.g. plant shoots or parts of shoots for micropropagation. Micropropagation of planting material uses the techniques of plant tissue culture and applies them to the propagation of plants. Micropropagation normally uses either shoots or shoot tips or other vegetable plant organs as starting points. At its simplest, micropropagation consists initially of excising small a pieces of actively growing tissue. Then, under sterile conditions, the pieces of tissue are transferred to a nutrient medium which supports plant growth. The plant ma.terial will finally develop into entire plantlets. These plantlets must then be weaned from the axenic conditions in which they have existed within the laboratory into viable, rooted plants capable of survival in conventional horticultural or agricultural enviroments.

The technique is labour-intensive, and two of the particularly important operations which are repeated frequently are (i) cutting a required propagule of plant tissue from a donor plant or culture, and (ii) picking up the required piece of plant material, transferring it to a soft, nutrient medium, and placing it in such a manner that it stands upright. As performed at present, the cutting operation normally consists of an operator holding the plant material by forceps on a sterilised card by one hand, and cutting the required portion of the plant by strokes of a scalpel, by the other hand. Commonly, three cuts are required to cut from the donor plant shoot a node at which a side-shoot has developed from an axillary bud. The cut portion is then transferred by forceps to the soft nutrient medium, which is in the nature of a gel, and the cutting is then manoeuvered so as to stand upright with the stem part of the cutting in the soft nutrient medium. The manoeuvering is normally carried out by the use of forceps. The high cost of these labour intensive operations has meant that micropropagation techniques have been limited to plant species which attract an adequate premium for greater uniformity or vigour, or are difficult or impossible to propagate from seed or cuttings. It is an object of the present invention to provide apparatus and methods for effecting cutting and manoeuvering operations involved in micropropagation techniques, either manually with greater speed and less reliance on operator skill, or by the use of an automatic or semi-automatic robotic system. This will allow the benefits of micropropagation to be utilised in the growth of more plant species where it is at present prohibited by the costs involved.

In accordance with a broad aspect of the invention, there is provided a method of cutting plant tissue for micropropagation comprising the steps of pressing together a cutter and plant tissue to be cut, retaining in a recess in the cutter a cut part of the plant tissue and releasing the cut part of the plant tissue from the recess at a required location over a propagation medium. A corresponding apparatus for carrying out these steps is also provided.

In accordance with a preferred aspect of the present invention there is provided a method of cutting plant tissue for micropropagation comprising the steps of pressing together plant tissue to be cut and a cutter having a substantially circular cutting edge, rotating the cutting edge relative to the plant tissue while pressing the cutter and the plant tissue together, retaining in a recess in the cutter a cut part of the plant tissue which lies within the substantially circular cutting edge, and releasing the cut part of the plant tissue from the recess at a required location over a propagation medium.

Although it is preferred that the substantially circular cutting edge is a continuous circular cutting edge, it is to be appreciated that the edge may be interrupted, so as to be part circular, or may differ slightly from a true circle, so long as the overall effect is that rotation of the cutter produces cutting of the item as required.

Conveniently the cutter comprises a cylindrical blade and the recess is formed in the interior of the cylinder. The means for pressing and rotating the cutting edge may comprise a handle for manual operation of the device, or may comprise a driven support means for moving the cutter to a required cutting position and pressing and rotating the cutting edge under remote control. The remote control may either be under the direction of a human operator, or may be directed as part of an automatic or semi-automatic robotic system.

Normally the pressing together of the plant tissue and the cutter, and the relative rotation of the cutter, is achieved by the steps of supporting the plant tissue on a stationary support, moving the cutter relative to the support, and rotating the cutter relative to the support, while continuing to move the cutter towards the support. However it is to be appreciated that various other forms of relative movement may be used, for example by the cutter being rotated relative to a stationary frame, and the plant tissue being raised relative to the frame towards the rotating cutter.

In a preferred form, the method includes the steps of positioning the substantially circular cutting edge over a node on a plant, and rotating the cutting edge so as to effect a cut below the node through the plant stem, and one or more cuts above the node through the stem and/or one or more side growths. For example, the method may include the steps of positioning the substantially circular cutting edge over a node on a plant shoot, and rotating the cutting edge so as to effect three cuts in the plant shoot, one below the node through the plant stem, and two above the node through the stem and through a petiole.

Normally the method will include the step of moving the circular cutting edge together with the cut part of the plant within the circular cutting edge, to a required location over a propagation medium, and releasing the cut part of the plant from the recess, although in other arrangements the propagation medium may be moved to the cutter. The cut part of the plant may conveniently be expelled from the recess by relative movement between a pushing member within the recess, and the said cutting edge.

In a preferred form, the method may include releasing the cut part of the plant over a soft propagation medium with the cutting lying flat on the surface of the medium, and pushing downwardly one end of the cutting into the medium, so as to tip the plant cutting upright with one end of a stem of the cutting in the medium. Preferably the tipping is achieved by positioning over the plant cutting a lateral projection which projects laterally from a shaft of a tool, and pushing the shaft of the tool downwardly so as to tip the plant cutting upright with one end of the stem of the cutting in the medium. Preferably the method includes the step of withdrawing the tool by moving the tool firstly away from the plant cutting by moving the tool laterally in a plane approximately containing the cutting and the lateral projection of the tool, without substantial vertical movement, and secondly moving the tool and the soft propagation medium apart.

The method of the invention has particular application where the step of pressing the cutter against the plant shoot is effected by remote control by a driven support means for moving the cutter to a required cutting position and for pressing and rotating the cutting edge by an operator controlling the drive means remotely. in one form of the method, suitable for remote control, the method includes the steps of expelling the cut part of the plant from the recess at a required location over a soft propagation medium by moving from within the recess a tool comprising a shaft and a lateral projection projecting laterally from the shaft, the lateral projection being positioned (either before or after expulsion) over the stem of the plant cutting and pushing the shaft of the tool downwardly so as to tip the plant cutting upright with one end of the stem of the plant in the medium. There is also provided in accordance with the invention in a broad aspect apparatus for cutting plant tissue for micropropagation comprising a cutter, first drive means for arranging the cutter at a position over the plant tissue, second drive means for pressing the cutter and the plant tissue together, the cutter having a recess for retaining the cut part of the plant, and means for releasing the cut part of the plant at a required location.

There is also provided in accordance with a preferred form of the present invention apparatus for cutting plant tissue for micropropagation comprising a cutter having a substantially circular cutting edge, first drive means for arranging the cutter at a position over the plant tissue, second drive means for pressing the circular cutting edge and the plant tissue together and rotating the cutting edge relative to the plant tissue, the circular cutting edge having a recess in the cutter for retaining the cut part of the plant which lies within the circular cutting edge, and means operable within the recess for expelling the cut part of the plant out of the recess at a required location. Preferably the cutter comprises a cylindrical blade and the recess is formed in the interior of the cylinder. Also preferably the expelling means comprises a pushing member within the recess mounted for relative movement between the pushing member and the cutter to push the cut part of the plant out of the recess.

The apparatus may include as part of the apparatus a tool for manoeuvering the plant cutting when lying on a soft propagation medium, comprising a shaft, a lateral projection from the shaft shaped to lie over a plant cutting lying on a soft propagation medium, and means for moving the shaft downwardly so as to tip the plant cutting upright with one end of the cutting in the medium.

In accordance with another independent aspect of the invention, there is provided a tool for manoeuvering a plant cutting lying on a soft propagation medium, comprising a shaft, a lateral projection from the shaft shaped to lie over a plant cutting lying on a soft propagation medium, and means for moving the shaft downwardly so as to tip the plant cutting upright with one end of the cutting in the medium. in a preferred form, the lateral projection includes a downwardly facing concave portion adapted to locate over a stem of a plant cutting.

Conveniently the shaft and lateral projection are formed by a single member bent at the end in an upward curve leading sideways followed by a downward curve leading sideways, so that the lateral projection is generally formed in the shape of an £5 laid on its side.

The means for moving the shaft downwardly may comprise a handle for manual operation of the tool, or may comprise driven support means for moving the lateral projection to a required position, locating the lateral projection over a plant cutting, and moving the shaft downwardly to tip up the cutting, all these operations being carried out by remote control. There is also provided in accordance with this aspect of the invention, a method of positioning a plant cutting in a required orientation in a soft propagation medium, comprising the steps of placing the plant cutting on the medium with the cutting lying flat on the medium, and pushing the stem of the cutting downwardly so as to tip the plant cutting upright with one end of the stem of the cutting in the medium.

Conveniently the method includes the steps of positioning over the plant cutting a lateral projection which projects laterally from a shaft of a tool, and pushing the shaft of the tool downwardly. Preferably the method includes the step of withdrawing the tool by firstly moving the lateral projection sideways substantially without any vertical movement, away from the plant cutting, and secondly withdrawing the tool by moving the lateral projection vertically relative to the medium.

In accordance with another aspect of the invention, there may be provided a device for cutting and manoeuvering plant tissue for micropropagation, comprising a cutter having a substantially circular cutting edge, means for pressing the circular cutting edge against a plant shoot to be cut and rotating the cutting edge, a recess in the cutter for retaining the cut part of the plant which lies within the circular cutting edge, and means operable within the recess for expelling the cut part of the plant out of the recess, the expelling means comprising a shaft, and a lateral projection from the shaft shaped to lie over the plant cutting when lying on a soft propagation medium after being expelled from the recess, the said expelling means being adapted to move the shaft downwardly so as to tip the plant cutting upright with one end of the cutting in the medium.

There is also provided in accordance with this aspect of the invention, a method of cutting a plant shoot for micropropagation comprising the steps of pressing against the plant tissue a cutter having a substantially circular cutting edge, rotating the cutting edge to cut a part of the plant, retaining in a recess in the cutter the cut part of the plant which lies within the circular cutting edge, positioning the said cut part to a required location over a soft propagation medium, expelling the cut part of the plant from the recess by moving from within the recess a tool comprising a shaft and a lateral projection projecting laterally from the shaft, the lateral projection being positioned (either before or after expulsion) over the stem of the plant cutting and pushing the shaft of the tool downwardly so as to tip the plant cutting upright with one end of the stem of the plant in the medium.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:-

Figure la shows a typical plant from which a portion is to be cut;

Figure lb shows a typical node at a stem section to be cut from the plant;

Figure 2 is a diagrammatic cross-section through a cutting device embodying the invention; and

Figure 3 is a side view of a tool for manoeuvering a plant cutting, embodying the invention; Figure 4 is a diagrammatic cross-section through a tool for cutting and manoeuvering a plant cutting, embodying the invention, and combines features from the devices shown in Figures 2 and 3; Figure 5 is a diagrammatic cross-section of a cutting device embodying the invention, and shows a modification of the device of Figure 2 in which rotary motion is applied automatically to a cutter;

Figure 6 is a diagrammatic representation of an automatic or semi-automatic robotic system for cutting and manoeuvering plant cuttings.

Figure la shows in diagrammatic form a typical plant from which a tissue culture is initiated. The plant shown is, for example, a seedling, comprising a shoot tip region A, a stem region J3, and a cotyledon region C_. From the seedling a typical requirement for micropropagation is to cut the stem just above the cotyledons and cut the shoot into 1 cm stem sections with one node in each section. The stem sections each containing a node are then transferred to a nutrient medium and the cotyledon is discarded. It will be appreciated that in practice the method of the invention will normally be applied to plant tissue which has itself been micropropagated from an original seedling or other plant tissue. The seedling shown in Figure la is illustrated to show the structure of a typical plant. In Figure lb, there is shown a typical stem section which has been cut from a plant, to include a node. The cutting of tissue is indicated by the reference numeral 11, and the node indicated at 12. As _Can be seen in Figure lb, three cuts are required to remove the stem section, the cuts being shown at 13, 14 and 15. In accordance with the invention, the cuts are made by a circular cutting edge which effects the cuts at a position indicated at 16. in Figure 2 there is shown a device for cutting plant shoots for micropropagation, although the device may find use in cutting other plant tissue. The device 17 is conveniently approximately 14 cm long and has a main barrel 18 of outer diameter of 7 mm. The barrel 18 has an enlarged section at 19 into which is fitted as a push-fit a cylindrical cutter blade 20 having a circular cutting edge 21. Within the cylindrical cutting blade 20 is a recess 22. The main barrel 18 is conveniently ribbed or knurled at the end remote from the cutter 20, to allow rotation of the barrel and cutter manually.

Within the main barrel 18 is a shaft 23 which is a loose sliding fit within the barrel 18. At the upper end the shaft 23 carries a Push-button 24 protruding from the main barrel 18, and at the lower end the shaft 23 carries a cylindrical collar 25 which is a push-fit onto the end of the shaft 23. A spring 26 acts between a shoulder 27 at the inner end of the push-button 24, and a shoulder 28 at the upper end of the bore 29 through the barrel 18. A further push-fit collar 30 at the lower end of the shaft 23 limits the upward travel of the shaft.

In operation the cutting device is held manually and placed over the plant tissue to be cut and is lowered to press the circular cutting edge 21 against the plant and against a support which may conveniently be a sterilised card. The barrel 18 and cutter 20 are rotated manually to effect the cut along the circle 16 shown in Figure lc, and the device 17 is then lifted carrying with it the cut stem section 11 which becomes lodged in the recess 21 inside the cylindrical cutter. 20. The cut culture is then transferred to a required propagation medium on which it is placed by depression of the push-button 24 so that the collar 25 pushes the plant culture free of the cutter 20 onto the top surface of the gel-like propagation medium. T e next stage in operation involves use of a tool

31 which is shown in Figure 3. The tool has a handle

32 which terminates in a shaft 33 which is bent sideways to provide a lateral projection 34. The projection has an upward curve 36 followed by a downward curve portion 37 and has the overall shape of a letter S_^ on its side. The portion 37 provides a downwardly facing concave curved portion which is adapted to be placed over the stem of the section of plant culture 11 shown in Figure lb, at the dotted line 38. The curved section 37 of the tool fits over the stem of the culture 11, and when the tool 31 is pressed downwardly, the cutting is tipped upwardly so that the stem end 39 enters into the medium, to allow absorption of nutrients.

It is to be appreciated that the shape of the tool in Figure 3 is chosen so that the main shaft 33 is off-set from the curved section 37. This is done so that the shaft 33 does not contact or interfere with the main portion of the cutting 11 while it is being tipped up, as would be the case if the tool had the shape, for example, of a conventional pitchfork. in a modification of the embodiment described so far, the cutting device and the manoeuvering tool of Figures 2 and 3 are combined, so that the shaft 33 of the tool 31 replaces the lower end of the shaft 23 in the cutter device 17. Thus instead of the collar 25 for pushing the plant cutting out of the cylindrical cutter 20, the expulsion of the plant cutting is carried out by the lateral Projection 34 on the shaft 33. After the plant cutting has been ejected, the lateral projection 34 is then used to tip-up the plant cutting in the way which has been described previously.

Such a combined device is shown in Figure 4, and components which correspond to components in Figures 2 and 3 are indicated by like reference numerals. It will be seen that the shape of the shaft 33 and lateral projection 34 has been modified in Figure 4, from Figure 3, in that the shaft 33 is inclined sideways from the main shaft 23. The purpose of this is to position the lateral projection 34 substantially centrally below the axis of the shaft 23, whilst still providing the required off-set of lateral projection 34 from the shaft 33 so that when the plant cutting is tipped upright, it is not interfered with by the shaft 33. The lateral projection 34 is easier to use if it lies on the longitudinal axis of the shaft 23. Another aid to manoeuvering the plant is that a position indicator 37 projects sideways from the push button 24 and lies in the same plane as the plane of the lateral projection 34. This allows correct positioning of the curved portion 37 over the plant cutting before depressing the button 24. When using the planting tool of Figures 3 or 4, or other corresponding embodiments of the invention, it is important for consistant performance that the tool is withdrawn after erection of the plant cutting, in two stages. First the manoeuvering tool is moved laterally in the approximate plane which contains the erected plant cutting and the lateral projection 34 without substantial vertical movement. When the lateral projection 34 is clear of the plant cutting, it is then raised vertically, or by a movement including a vertical component. This manoeuvre avoids the plant cutting attaching to the lateral projection 34 by surface tension effect, which would tend to lift the plant cutting out of the nutrient medium.

Returning to the first stage of use of the combined tool of Figure 4, it is first necessary to position the curved portion 37 so that it straddles the basal portion of the plant cutting in a plane substantially perpendicular to the axis of the lower part of the stem of the cutting. This is achieved by use of the position indicator 37. It will also be noted that the tip of the ring cutter 20 is in substantially the same horizontal plane as the base of the lateral projection 34. The purpose of this is that when the cutter 20 is rotated, the_. lateral projection 34 will retain the required orientation in relation to the stem of the plant cutting. In an alternative arrangement_. (not shown) the main shaft 23 may be lowered by depressing the button 24 in two steps, against a double rate spring.

In Figure 5 there is shown a modification of the cutting device of Figure 2 , which is intended for use in an automatic or semi-automatic robotic system. In Figure 5, components corresponding to components in Figure 2 are indicated by like reference numerals. The cutting device is mounted in a main housing 40 having three stationary support plates perpendicular to the longitudinal axis of the housing 40, namely an upper end plate 42, a cross support 46, and a lower end plate 51. The main pusher shaft 23 of the device (which corresponds to the pusher shaft 23 shown in Figure 2) is, in the embodiment of Figure 5, stationary relative to the main housing 40. In the embodiment of Figure 5, the cutter blade 20 (corresponding to the cutter blade 20 in Figure 2) is moveable relative to the stationary pusher shaft 23. Thus the required relative movement between the pusher shaft and the cutter blade 20, is achieved in Figures 2 and 5 by reversing the moving and stationary main parts of the apparatus. Another main difference between the embodiment of Figure 5 and Figure 2, is that the required rotary motion of the cutter blade 20 is achieved automatically, whereas in Figure 2, the cutter blade 20 is rotated manually. Referring to Figure 5, a pneumatic piston and cylinder 43 and.41 respectively is mounted at the top of the assembly on the upper end plate 42. The lower end of the piston 43 is coupled through a spring and ball arrangement 52 and 53 to an adaptor 44 which is moveable downwardly relative to the housing 40 and the stationary cross support shaft 46. The adaptor 44 has a bearing 47 through which it is coupled to the main barrel 18 in which the cutter blade 20 is mounted. A corresponding bearing 54 is provided between the lower end of the main barrel 18 and a helical nut housing 50 which is mounted on the main housing 40 and lower end plate 51, to be held stationary relative thereto.

The main barrel 18 has on its external surface a helical thread at region 48, which co-operates with a mating helical nut 49 mounted in the housing 50 to be stationary relative thereto. Thus the arrangement allows vertical up and down movement of the adaptor 44 the barrel 18 and the cutter 20, relative to the stationary housing 40 cross support 46 lower end plate 51 and stationary pusher shaft 23. The bearings 47 and 5'4 allow rotation of the main barrel 18 and cutter blade 20 relative to both the stationary housing 40, and the moving adaptor 44.

In operation the main longitudinal axis of the apparatus is positioned over the node 12 (Figure lb) to be cut, and air pressure is supplied to the pneumatic cylinder 41. The pneumatic piston 43 carries the adaptor 44 downwardly and the mating helical nut 49 and helix 48 produce a downward and rotational movement of the cutter blade 20, which cuts the required part of the plant cutting. The entire housing 40 is then raised lifting the captured plant cutting 11 in the recess in the cutter blade 20, and the entire housing 40 is transferred to a position over the required nutrient. The air pressure is then removed from the pneumatic cylinder 41 so as to raise the pneumatic piston 43 so that the cutter blade 20 rises relative to the pusher shaft 23, whereupon the plant cutting is pushed out of the blade 20 by the end of the pusher shaft 23.

In an alternative method of operation of the device of Figure 5, the air pressure in the pneumatic cylinder 41 can be reduced in two stages after the plant cutting has been cut. At a first stage of reduction the cutter blade 20 is raised sufficiently to lift the cut plant cutting from the remnants of the plant material, but not so far as to bring the pusher shaft into operation. The entire assembly can then be moved to a required location over a soft nutrient medium. The second stage of reduction of the pressure in the pneumatic cylinder 41 can then be carried out, so as to operate the pusher member 23 to release the cut plant cutting.

Referring to Figure 6, there is shown an automatic or semi-automatic apparatus 60 for cutting and manoeuvering plant material for micropropagation. A main support base 61 carries two conveyor belts 62 and 63 driven by motors controlled by control lines indicated diagrammatically at 64 and 65 leading to a first control device 66.

Positioned above the conveyor 62 is a first robotically controlled Cartesian drive means 67 mounted on orthogonal pairs of tracks 68 and 69 and allowing in known manner a mobile carriage 70 to be positioned at any required position over the conveyor 62. Drive motors are provided at 71 and 72 and are linked by lines shown diagrammatically at 73 and 74, leading to a second control device 75. A similar second robotic drive means 76 positions a moveable carriage 77 over the second conveyor belt 63, by movement along tracks 78 and 79 under the control of motors 80 and 81. Control lines 82 and 83 control the motors 80 and 81, and lead to a third control device 84.

A first video camera 85 is positioned over the conveyor 62, and supplies video signals to a monitor 86. A second video camera 87 is mounted over the conveyor belt 63, and supplies video signals to a monitor 88.

Mounted on the carriage 70 is a cutting device 17 for example such as shown in Figure 5. The pneumatic operating device of the cutting device 17 is controlled by a pneumatic line 90 leading to a fourth control device 91.

Mounted on the second carriage 77 is a planting tool 31, which is not shown in detail but corresponds generally to the hand tool shown in Figure 3. In addition, there is provided a pneumatic cylinder arrangement similar to that shown in Figure 5, which allows the tool of Figure 3 to be raised and lowered under control of a pneumatic line 91 leading to a fifth control device 92.

In operation the plant material to be cut is placed on the conveyor 62 by means not shown and is carried to a position within the working range of the carriage 70. The carriage 70 is positioned by a first operator observing the monitor 86, and operating the first control device 66, second control device 75, and fourth control device 91. With the conveyor belt 62 stationary, the first operator positions the cutting device 17, lowers the cutter, cuts the required plant cutting, and raises the cut material captured in the recess in the cutter. The first operator then moves the plant cutting to the second conveyor 63, and deposits the plant cutting in a soft nutrient medium. This process is repeated until a tray of nutrient is filled with cuttings.

Next, the same operator, or a second operator, moves the tray containing the plant cuttings to the region of operation of the second carriage 77, by control of the first control device 66. The operator then positions the planting tool 31 over each plant cutting in turn, lowers the planting tool 31, and tips the plant cutting upright. The planting tool 31 is then withdrawn as has been described previously. n a modification of the system described, a fully automatic system can be produced in which a main control device 93 is fed with information (as shown by dotted lines) from the control devices 66, 75, 84, 91 and 92, and from the video cameras 85 and 87. The main control device 93 may then be arranged to provide a completely automatic system for identifying and locating plant material, cutting a required node therefrom, transferring the plant cutting to a nutrient medium, and tipping the plant cutting upright in the . nutrient medium.

It will be appreciated that the system shown in Figure 6 can be modified so as to incorporate the combined cutting and tipping tool shown in Figure 4.

Claims

1. A method of cutting plant tissue for micropropagation comprising the steps of pressing together a cutter and plant tissue to be cut, retaining in a recess in the cutter a cut part of the plant tissue, and releasing the cut part of the plant tissue from the recess at a required location over a propagation medium.

2. A method of cutting plant tissue for micropropagation comprising the steps of pressing together plant tissue to be cut and a cutter having a substantially circular cutting edge, rotating the cutting edge relative to the plant tissue while pressing the cutter and the plant tissue together, retaining in a recess in the cutter a cut part of the plant tissue which lies within the substantially circular cutting edge, and releasing the cut part of the plant tissue from the recess at a required location over a propagation medium.

3. A method according to claim 2 including the step of positioning the substantially circular cutting edge over a node on a plant shoot, and rotating the cutting edge so as to effect three cuts in the plant shoot, one below the node through the plant stem, and two above the node through the stem and through a petiole.

4. A method according to claim 2 including the step of expelling the cut part of the plant from the recess by relative movement between a pushing member within the recess, and the said cutting edge.

5. A method according to claim 2 including releasing the cut part of the plant over a soft propagation medium with the cutting lying flat on the surface of the medium, positioning over the plant cutting a lateral projection which projects laterally from a shaft of a tool, pushing the shaft of the tool downwardly so as to tip the plant cutting upright with one end of the stem of the cutting in the medium, and withdrawing the tool by moving the tool firstly away from the plant cutting by moving the tool laterally in a plane approximately containing the cutting and the lateral projection of the tool, without substantial vertical movement, and secondly moving the tool and the soft propagation medium apart.

6« Apparatus for cutting plant tissue for micropropagation comprising a cutter having a substantially circular cutting edge, first drive means for arranging the cutter at a position over the plant tissue, second drive means for pressing the circular cutting edge and the plant tissue together and rotating the cutting edge relative to the plant tissue, the circular cutting edge having a recess in the cutter for retaining the cut part of the plant which lies within the circular cutting edge, and means operable within the recess for expelling the cut part of the plant out of the recess at a required location.

7. Apparatus according to claim 6 in which the expelling means comprises a pushing member within the recess mounted for relative movement between the pushing member and the cutter to push the cut part of the plant out of the recess.

8. Apparatus according to claim 6 including a tool for manoeuvering the plant cutting when lying on a soft propagation medium, comprising a shaft, a lateral projection from the shaft shaped to lie over a plant cutting lying on a soft propagation medium, and means for moving the shaft downwardly so as to tip the plant cutting upright with one end of the cutting in the medium.

9. Apparatus according to claim 8 in which the lateral projection includes a downwardly facing concave portion adapted to locate over a stem of a plant cutting, the shaft and lateral projection being formed by a single member bent at the end in an upward curve leading sideways followed by a downward curve leading sideways, so that the lateral projection is generally formed in the shape of an S_^ laid on its side.

10. Apparatus according to claim 8 in which the said shaft and lateral projection for tipping the plant cutting, are housed within the recess in the cutting means, and are mounted to be moveable relative to the circular cutting edge.

11. A tool for manoeuvering a plant cutting lying on a soft propagation medium, comprising a shaft, a lateral projection from the shaft shaped to lie over a plant cutting lying on a soft propagation medium, and means for moving the shaft downwardly so as to tip the plant cutting upright with one end of the cutting in the medium.

12. A method of positioning a plant cutting in a required orientation in a soft propagation medium, comprising the steps of placing the plant cutting on the medium with the cutting lying flat on the medium, and pushing the stem of the cutting downwardly so as to tip the plant cutting upright with one end of the stem of the cutting in the medium.

13. A device for cutting and manoeuvering plant tissue for micropropagation comprising a cutter having a substantially circular cutting edge, means for pressing together the circular cutting edge and a plant shoot to be cut and rotating the cutting edge relative to the plant shoot, a recess in the cutter for retaining the cut part of the plant which lies within the circular cutting edge, and means operable within the recess for expelling the cut part of the plant out of the recess, the expelling means comprising a shaft, and a lateral projection from the shaft shaped to lie over a plant cutting when lying on a soft propagation medium after being expelled from the recess, the said expelling means being adapted to move the shaft downwardly so as to tip the plant cutting upright with one end of the cutting in the medium.