Abstract:
A method of collecting secretions from trees including making a predetermined shaped incision through the bark to the surface of the wood and applying a secretion flow activation agent to the incision. The method further includes placing a receptacle in the incision, wherein the receptacle comprises a lower outer part and a flow tube portion located at the lower outer part, and wherein a portion of the receptacle has the same shape as the predetermined shape of the incision. The method further includes fixing a collecting apparatus to the flow tube and subsequently removing the collecting apparatus from the flow tube when the collecting apparatus contains secretions from the trees. The method still further includes closing the collecting apparatus, storing it in a container, closing the container, transporting the container to a product recovery site, cleaning the closed collecting apparatuses at the product recovery site, opening the clean collecting apparatuses, and recovering the secretions from the clean collecting apparatuses.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the collecting of products secreted by trees and refers more particularly to improving the harvesting of pins resin, or oleoresin, produced by coniferous trees (for example:  pinus pinaster, pinus eliattii, pinus sylvestris, pinus nigra, pinus pinea, pinus palustris, pinus edulis, pinus canariensis, pinus merkusii, pinus kashya , etc.), when their bark is cut sufficiently deeply to reach the surface of the wood. 
     DESCRIPTION OF RELATED ART 
     The outflow of such products enables the tree to protect itself against its natural enemies (insects, fungi, etc.) by producing a layer of oleoresin which dries in air by the evaporation of the volatile part which it contains, thereby forming a crust which will enable the bark to grow back again A region forms around the incision that is very rich in channels that secrete this oleoresin, especially from the top of the incision, since the outflow follows gravity. 
     The constituents of the oleoresin, monoterpenes and resinic acids, are of very great industrial importance in many different flourishing sectors, such as the synthesis of raw materials for perfumes, inks, adhesives and so forth. 
     The object of the invention is to provide a method of collecting the resin in such a way that these products can be obtained at a price that will compete with raw materials produced from petroleum without diminishing the quality of the wood of the trees. 
     By contrast, currently used methods harvest only some of the outflow, partly by allowing the secretory channels to become blocked and partly by allowing the volatile products, whose industrial value is very considerable, to evaporate into the air. Furthermore, the systems generally employ placing metal parts into the wood, the presence of such parts is undesirable for the wood conversion industry. 
     In patents FR 691,361, FR 725,773 and FR 725,774, a method is described for tapping secretions using a manual mechanical apparatus enabling the tree to be prepared in order for a “closed” oleoresin tapping system to be placed against it. 
     Patent FR 2,746,582 discloses a closed-vessel tapping system applied to the technique of traditional hand resin-tapping and film distillation of the oleoresin on the harvesting site, in a specially equipped vehicle. 
     Patents U.S. Pat. No. 3,959,925 and U.S. Pat. No. 4,291,492 disclose tractors possessing complex mechanized jointed-arm systems for making incisions in the bark of trees and applying an activator, but according to A. W. Hodges &amp; W. D. Shoup (Naval Stores Review, 1988, July/August, pp. 13-19), their profitability is low, being directly connected to the firmness and flatness of the ground and their cost is high. 
     Many patents disclose systems for activating the secretion of the oleoresin, generally employing sulphuric acid, as noted by Prof. G. Stephan in Naval Stores Review, 1990, November/December, p. 13. To take one example, patent FR 2,160,742 discloses a solution containing sulphuric acid and a lignosulphonate. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the invention is to devise a collecting method that will make it possible to bring about the greatest possible outflow of product from the secretory channels of the tree. 
     It is also an object of the invention to devise a collecting method that makes it possible to limit the work on the tree, enabling each person to operate on the greatest possible number of trees per unit time, during the preparation of the tree by making an incision in the bark and for harvesting the product, while avoiding the current practice of removing bark at the start of the season and harvesting the barras resin at the end of the season. 
     It is also an object of the invention to devise a method of collecting the greatest possible amount of expressed oleoresin in as pure a state as possible in order to obviate the need for subsequent processing, the cost of which is prohibitive. 
     For this purpose the resin must be protected, as it emerges from the surface of the tree, from rubbish (bits of bark, branches, insects, etc.) and from rainwater which would carry away the tannins present in pine bark. 
     Similarly, the method of the invention seeks to limit the evaporative losses of the essences (terpenes) whose volatility is sufficient to greatly reduce the yield of the harvest. The method of the invention seeks furthermore to make it possible to obtain a high-quality product with limited oxidation of the oleoresin in the presence of air, water and ultraviolet light emitted by the sun. 
     The subject of the invention is therefore a method of collecting products secreted by trees, particularly for pine resin or oleoresin produced by coniferous trees, the method comprising the following steps: making an incision in the tree trunk of sufficient depth to reach the surface of the wood; applying to the incision a product to activate the outflow of the product to be tapped; placing in the incision a receptacle of corresponding shape, in the lower outer part of which is an outflow tube; characterized in that it also consists in fixing to the outflow tube of the receptacle a collecting bag made of a plastic that is resistant to the product collected; removing the bag when filled with product and closing it; storing the closed bags in a container and closing the container when filled with bags; transporting the closed container to a product recovery site; treating the bags contained in a container in order to clean their exterior soiled in the course of the product collecting operation; opening the cleaned bags; and recovering the product which they contain. 
     The invention also relates to a product collecting bag for carrying out the method according to the technique defined above, characterized in that it comprises a fixing means that fits the shape of the end of the outflow tube of the receptacle. 
     The invention also relates to an apparatus for making incisions in the trunk of a tree for carrying out the collecting method according to the technique defined above, characterized in that it comprises a frame with means for fixing it temporarily to the bark of the trunk and manual means for holding the frame fixed to the trunk, a rotary cutting tool that can be displaced at least axially on the frame and, mounted on the frame, a drive motor for rotating the cutting tool. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A clearer understanding of the invention will be gained from the following description, given purely by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of an apparatus for making incisions in a tree trunk, according to the invention; 
     FIG. 2 is a bottom view of a router bit used in the apparatus of FIG. 1; 
     FIG. 3 is a side view of the router bit of FIG. 2; 
     FIG. 4 is an exploded perspective view of a first embodiment of resin-collecting means according to the invention; 
     FIG. 5 is a side view in section of a second embodiment of the resin-collecting means according to the invention; and 
     FIG. 6 is a sectional view of another embodiment of an apparatus for making incisions according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a perspective view of an apparatus for making incisions in a tree trunk. It comprises a frame I in the general form of an open rectangle comprising two curved sides  2  for adapting to the curvature of tree trunks. They are consequently intended to be placed roughly horizontally. 
     The other two sides  3  of the frame  1  are straight and each has a handle  4  for holding the frame against the trunk in question. 
     The frame is provided with means for fixing it temporarily to the bark of the tree trunk in the present example these means are conical spikes  5  arranged at the four corners of the frame. 
     The taper of the spikes  5  is such as to allow them to be pushed relatively easily into the back of the trunk and to allow the frame to be held in place while allowing the apparatus to be withdrawn without any particular effort. 
     In other embodiments the frame may also be made square, triangular or of a rounded, concave shape as in FIG. 1, or flat. 
     The number of fixing means may be other than four. 
     An arrangement with three conical spikes arranged at 120° relative to the centre of the frame may be advantageous. 
     The material of the frame is selected for sturdiness and low weight. For example, the frame may be made from light alloy or steel. 
     In the space bounded by the open rectangle of the frame there are tubular rails  6  whose slope relative to the curved sides  2  of the frame is dependent on the orientation of the incision to be made in the trunk. The rails  6  also have a curvature corresponding to that of the curved sides  2 . 
     Moving on the rails  6  is a carriage  7  at each end of which are two trains of grooved wheels  8 , which grip a corresponding rail  6  and thus keep the carriage on the rails and enable it to move along them. 
     A tubular column support  10  is mounted on the carriage  7  and contains a sliding column  12 . A drive shaft  14  rotates inside the column  12  and at its end nearest the frame it carries a cutting tool  16  consisting of a router bit which will be described in greater detail with reference to FIGS. 2 and 3. 
     At the end furthest from the frame  1 , the column  12  carries a casing  18  for a drive motor (not shown). 
     The end of the shaft  14  that enters the casing  18  is fitted with a coupling member  20  for coupling it to the output shaft of the drive motor. 
     This motor may be an electric motor or a heat engine. 
     In a variant, the heat engine may be separate from the apparatus and connected to it by a flexible drive. 
     Between the frame  1  and the casing  18  a helical spring  22  sits around the column support  10  and around the column  12  in order to return the column  12  and hence the tool  16  to the inactive position in which the latter is withdrawn inside a housing  24  provided in the carriage  7 . 
     The column  12  advantageously carries a collar  26  of adjustable axial position forming an end stop for the penetration of the tool into the trunk of the tree. 
     Referring now to FIGS. 2 and 3, the router bit  16  can be seen to be a bit with two diametrically opposite teeth  28  with cutting edges  29  curved in the direction of rotation of the bit and having cutouts  30  at their lower end as clearly shown in FIG.  3 . The cutouts  30  are designed to leave a rim of inner bark or of bark around the edge of the bottom of the incision. 
     The resulting profile of the bit gives an incision with an appropriate bottom and evacuates loose bark chips when making the incision. 
     The tool described above with reference to FIGS. 1 to  3  makes it possible to prepare a tree trunk with either a circular incision whose diameter corresponds to that of the router bit  16 , or an elongate incision whose width corresponds to the diameter of the bit  16  and whose length is determined by the travel of the carriage  7  along its guide rails  6 . 
     It is also possible to move obliquely relative to the curvature of the frame in order to vary the depth of the incision. 
     Two elongate incisions of the kind indicated above ire shown in FIG. 4, which is an exploded view of the various components of the collecting device by which the method of the invention is implemented. 
     The incisions  32 ,  33  are made in a trunk T with the apparatus shown in FIG. 1 after fixing the apparatus to the trunk with the aid of its conical spikes  5 , and engaging the rotating bit  16  in the bark of the trunk by axial movement of the column  12  counter to the action of the return spring  22 , followed by movement of the carriage  7  along the curved rails  6  fox a distance corresponding to the desired incision length. 
     A collecting receptacle  35  whose shape corresponds to that of the incision  32  is placed in the incision after it has been sprayed with a product that will activate the outflow (i.e., a flow activation agent). 
     The receptacle  35  is pushed into the incision  32  by hand or preferably with a mallet until it meets the inner bark. 
     The collecting receptacle is made of a plastic material resistant to resin, e.g. polypropylene, whether translucent or opaque, or any appropriate metal such as zinc. 
     It has an edge  36  which fits the curvature of the trunk and corresponds to the curvature selected for the shape of the frame  1  of the apparatus of FIG.  1 . 
     In one particular embodiment the receptacle, if made of plastic, is made by injection molding. 
     By its shape or with the aid of a metal piece (not shown) which is added to it, it forms a seal around the outflowing resin. 
     The receptacle  36  is produced from a flow at a low melting point of standard polypropylene, such as RD 369P from the company Borxalls. 
     The material has been chosen to satisfy the most important properties for the application envisaged, such as its flexural modulus, hardness, durability and transparency. 
     An ultraviolet stabilizer such as Civrasorb 9441 from the company Ciba has been added in order to extend the life of the receptacles in sunlight. 
     In the outer part of the receptacle  36  where it is intended to be engaged in the lower part of the incision  32  is an outflow tube  38  made of the same material as the receptacle and integral with it. The tube, which is of appropriate dimensions, e.g. from 5 to 30 mm in diameter and a few centimetres long, allows the resin to flow out freely under gravity. 
     A plastic collecting bag  40  is fixed to the tube  38 , which in the present example has an enlargement  39  molded integrally with the tube. 
     The bag  40  has a rigid and piece  42  welded to the bag with a recess (not shown) to accommodate the enlargement  39  on the outflow tube  38 . 
     The bag is made of a material suitable for the product collected. 
     It is in a form permitting a good outflow of the product collected, for example a sachet form or a gusseted form. 
     It is advantageously closed at both ends by sealed lines such as  44 . 
     The embodiment shown in FIG. 5 comprises a receptacle  46  in the form of an injection-molded funnel with a circular footprint which can be produced with the aid of the apparatus of FIG. 1 without displacing the tool along the tracks  6  of the frame or by a similar apparatus without means of moving the tool around the trunk. 
     This receptacle comprises an outflow tube  48  on whose free end is a small annular enlargement  50  for retaining a rigid ring  52  welded to a collecting bag  54 , to which a cap  58  is connected by a flexible tag  56  for closing the collecting bag when full and removing it from the outflow tube  48 . 
     The bag is a advantageously made of polypropylene. 
     It has gussets such as the gusset  59  on each side. 
     The fixing of the bag to the outflow tube can be done using any fixing means comprising a rigid piece  41  one end of which clips onto the bag  40  placed on the outflow tube  38 , while the other end forms a member  43  for closing the bag when the bag is full and withdrawn from the receptacle. 
     The bag  54  advantageously initially has no orifice inside the rigid ring  52 . It is fitted to the outflow tube  48  of the outflow receptacle  46  by perforating it. 
     The bag used according to the invention protects the resin from any external contaminant such as bits of bark, insect, air and water, because of the fact that the oleoresin is being recovered in a closed system. 
     The method of collection according to the invention is carried out as follows. 
     First of all, the tree is prepared. 
     In order to reduce the amount of movement around the forest, it is envisaged in this method that one, two or three incisions are made in each tree trunk at different orientations around the tree. 
     The incisions in accordance with the invention may be of varying shapes such as, for example, elongate, similar to those designed to take receptacles of the kind described with reference to FIG. 4, circular for taking receptacles such as that described with reference to FIG. 5, rectangular, triangular or square, and arranged horizontally, vertically or obliquely. The depth of an incision may vary linearly along its length or be of a convex or concave form or have predefined irregularities. 
     The method according to the invention limits the amount of time spent on the tree because there is no preparation of the tree prior to making the incision, there being no need to remove the bark. 
     Similarly, the step of recovering the barras, resin at the end of the season is dispensed with. 
     To increase the productivity of tree preparation, this operation is carried out by teams of two people, since it requires two separate successive functions to be carried out. 
     The first person or cutter makes the incision with the apparatus according to the invention described with reference to FIG.  1  and the second person, the installer, places the device in this incision so that the resin can be tapped with very high yield and excellent purity. 
     The cutter applies the easily transportable apparatus described with reference to FIG. 1 to the non-debarked tree at a height of between 0 and 200 cm from the ground. 
     The slope of the guide rails  6  of the carriage  7  relative to the frame  1  enables the incision to be given the desired shape and orientation. 
     The profile of the router bit  16  has its own function of determining the shape of the bottom of the incision and of evacuating the bark. 
     As indicated earlier, the frame is fixed temporarily to the trunk of the tree by pushing its conical spikes  5  into the tree bark. These spikes keep the apparatus fixed to the tree trunk and permit relatively easy withdrawal of the apparatus after the incision has been made. 
     Once the frame  1  is placed against the trunk, it is held in position by the handles  4 . The motor is then started and drives the shaft  14  on which the router bit  16  is mounted so that the latter rotates, and the column  12  is displaced relative to the frame  1  so that the bit  16  enters the bark of the trunk and produces an incision of circular cross section. The movement of the carriage  7  carrying the tool along the guide rails  6  of the frame  1  produces an incision of selected shape, e.g. elongate, such as the elongate incisions  32  and  33  shown in FIG. 4 
     If necessary, an oblique movement relative to the plane of the frame makes it possible to vary the selected depth of the incision. 
     When the operation of making an incision is finished, the return spring  22  moves the column  12  and consequently the router bit  16  translationally relative to the frame and at the end of the stroke the bit  16  is retracted into the housing  24  provided in the carriage  7 . 
     The depth of the incision ti dependent on each tree, the router bit  16  cutting into the inner bark but stopping when it meets the wood. 
     The diameter drilled out by the bit is from  2  to 10 cm and may advantageously be between 3 and 8 cm. 
     The curvature of the frame, that is to say the curvature of its curved sides  2 , has a radius of from 15 to 40 cm so as to fit the varied shapes and diameters of the tree trunks. 
     By means of the arrangement of the invention, the tool  16  makes a cut of constant depth relative to the bark along the entire length of the travel of the tool along the guide rails  6  of the carriage  7 . 
     The rapid rotation of the bit  16  and its particular profile ensure efficient evacuation of the bark chips removed by the bit as it forms the incision. 
     The result of all this is a clean incision of a selected and highly precise form, done in a very short time of less than 10 seconds, preferably lest than 8 seconds. 
     The apparatus described with reference to FIG. 1 is characterized by its low weight, its small size, its fast operation, the accuracy and repeatability of the shape of the incisions produced, and its simplicity. 
     Furthermore, the apparatus is ergonomic. 
     By virtue of the shape of the router bit  16  described in detail with reference to FIGS. 2 and 3, a neat and tidy cut is made in the resin-secreting channels, thus ensuring an easy outflow of the oleoresin. 
     This advantage can only be maintained over time by applying to the incision, e.g. by spraying, a product that prevents crystallization of the resin and does not harm the tissues of the tree. 
     The installer applies this product to the top cut of the incision, this being the area that produces the most resin, and with a view to further incisions which will be made above the earlier incisions. 
     The installer immediately closes the opening of the incision with a receptacle such as the receptacle shown in FIG. 4 or that shown in FIG. 5 depending on the shape of the incision, using the apparatus shown in FIG.  1 . 
     As indicated above, the receptacle  35  or  46 , depending on its shape, is driven in by hand or preferably with a mallet until it meets the wood. 
     Once the receptacle is in place, a collecting bag  40  (in the case of the embodiment of FIG. 4) or a bag  54  (in the case of the embodiment of FIG. 5) is fixed to it, the bag being fixed to the corresponding outflow tube  38 ,  48  and secured to this outflow tube by the means described with reference to FIGS. 4 and 5. 
     As can be seen, with the arrangement of the invention, the application of the resin recovery system is simple and rapid, and takes the same amount of time as is required to produce the incision. 
     According to the method of the invention, the cutter and the installer work at the same rate, thus avoiding the loss of time which would detract from the profitability of the resin collection process. 
     The work of the team is repeated three or four times in the course of the season, which runs from May to September, allowing an interval of about four to six weeks between each operation. 
     Each new incision is made above the previous one, leaving a gap of from 2 to 10 centimetres. This gap must correspond to the height necessary for the limit of action of the activator of the previous incision to appear on the wood. 
     Two harvests are carried out in the course of the season, one after the second incision and the other after the last. 
     The bags are easily removed from the receptacles by simply pulling them off by hand. 
     Each of these bags is immediately closed for example as regards the bag  54  of the embodiment shown in FIG. 5 by its cap  58 , or alternatively using a clip  41  in the case of the embodiment shown in FIG.  4 . 
     Thus closed, the bags are stored in fully open drums (hot shown). When a drum is full it is closed with a lid held by a hoop and taken away to a resin recovery site. 
     Bags collected in accordance with the method of the invention are sprayed or placed in a bath or steam-treated to clean their exterior, which will have become soiled during their period on the trees such as pines. 
     When cleaned, the bags can be opened for recovery of the resin. 
     Resin that stays on the bags is recovered by separating the oleoresin from the walls of the bag by warming them to between 50° C. and 90° C., and preferably between 60° C. and 80° C., the bags being hung open. 
     The plastic material selected for the bags is recyclable and, as indicated earlier, this material is advantageously polypropylene. 
     The resin recovered by the method of the invention is ready to be used industrially. 
     The harvesting of the resin according to the invention leaves behind no plastic or metal that will be harmful to the industrial use of the pine. In the method according to the invention all that is left on the tree is a vertical series of marks over an area of no more than 40 cm×15 cm, this limiting the impact of the operation on the quality of the wood. 
     EXAMPLE 1 
     An experiment to harvest resin from pinus pinaster trees was performed with an apparatus in which the steel frame is of rectangular shape, of dimensions 25×35 cm, fitted with two handles (FIG.  1 ). This frame is concave and its radius of curvature is about 30 cm, corresponding to the average size of the pine trees studied. 
     The face in contact with the tree bears spikes of different lengths ranging from 2 to 7 cm, of conical shape, and all parallel with each other. 
     Two tracks  6  reproducing the shape of the frame allow controlled movement of a mechanical tool consisting of the router bit  16  turned by an electric motor (not shown). The diameter of the bit is 40 mm and its shape is such that after having removed the bark, it is able to skid over the wood without biting into it. The bit  16  can be moved at right angles to this frame by pushing the tool column  12  towards the tree. 
     The return spring  22  returns the bit to it initial position when the pressure is removed. 
     The total weight of the apparatus is 6 kg. The supply to the electric motor is provided by batteries worn on the belt or by an electricity generating set on an individual off-road vehicle used for moving around the forest. 
     The apparatus was able to make incisions of identical form for each tree (FIG. 4) when a 4-cm diameter router bit was displaced over a distance of 9 cm. This displacement follows a slope of approximately 10° to the horizontal. 
     The incision is simultaneously cleaned by the rotation of the tool  16 . When the cutter has finished this work, the installer sprays on an activator, i.e. a secretion flow activation agent, of at least equal performance to that of the SICAGEM described in patent FR 2,160,742. 
     The installer then sets in position a polypropylene receptacle that exactly reproduces the shape of the incision and the curvature of the incision bottom. The receptacle used is translucent and has a pipe at its lower end (FIG.  4 ). A high-density polypropylene bag in the form of a sachet such as the bag  40  is then fixed to the receptacle by a clip system. This bag can hold up to 1.5 litres and is 20 cm wide by 30 cm from top to bottom. 
     In this way the team prepared 300 trees per day on average. 
     A first bag is harvested and closed after the end of the production of the second incision of the season, and a second bag at the end of the season on the last incision. 
     The bags are collected in fully-open 220-litre coated drums. Between 1 and 2.5 litres of resin are harvested per tree. 
     The full drums are closed and taken away to the resin processing centre. 
     The closed bags are steam-cleaned and then cut open automatically so that they can be emptied by hanging them over collecting containers. The operation is performed in an enclosure heated to 60° C. in order to recover all of the resin. The resin collected contains 70% rosin and 30 turpentine. 
     EXAMPLE 2 
     Identical to Example 1 but this time the incision-making apparatus is driven by a heat engine carried on the back of the user in an appropriate harness and connected to the column of the router bit by a flexible drive system (not shown). The weight of the engine is 3 kg, and that of the frame fitted with the bit is 4.5 kg. 
     EXAMPLE 3 
     Identical to Example 1 but this time the motor of the apparatus of FIG. 1 is a heat engine. 
     EXAMPLE 4 
     Identical to Example 3 but this time the frame of the apparatus is triangular, the sides being 45 cm in length. 
     EXAMPLE 5 
     Identical to Example 1 but this time the frame is circular and has a diameter of 20 cm. The shape of the incision is circular with a diameter of 8 cm, and the router bit has a diameter of between 4 and 8 cm. 
     The shape of the receptacle is identical to that of the incision (FIG.  5 ). 
     EXAMPLE 6 
     Identical to Example 1 but this time the incision is triangular with sides 9 cm long. 
     EXAMPLE 7 
     Identical to Example 1 but this time the bag is rectangular and gusseted. 
     In the example given below, the method of the invention will be carried out using the collecting means described with reference to FIG. 5, set in position on a circular incision made for example using an apparatus shown in FIG.  6 . 
     EXAMPLE 8 
     A circular incision is made with the apparatus shown in FIG.  6 . 
     This apparatus comprises a frame  60  in the form of a bell with two diametrically opposite curved arms  62  at its open end that extend symmetrically with respect to the bell  60  and have conical spikes  64  with which to fix the apparatus by driving them into the bark of a trunk. 
     The bell  60  has a tubular axial extension  65  inside which a column  66  is able to move axially. Inside the column  66  is a rotary shaft  67 , the end of which inside the bell  60  carries a router bit  68  of the type described with reference to FIGS. 2 and 3. 
     At the other end, away from the bell  60 , the column  66  supports a casing  70  for a heat engine (not shown) as a drive means. 
     Between the casing  70  and the bell  60 , a helical return spring  72  surrounds the column and has the same function as the spring  22  of the apparatus seen in FIG.  1 . 
     The bell  60  protects the router bit  68  when the latter is retracted into the inactive position inside the bell and it is perforated with openings  69  for the ejection of chips and dust. 
     It can be seen therefore that, as in the apparatus described with reference to FIG. 1, the router bit  68  rotated by the heat engine mounted in the casing  70 , via the shaft  67 , which for this purpose is provided with a coupling member  72  where it enters the casing  70 , can likewise be moved axially with the column  66  counter to the action of the return spring  72  in order to come into contact with the bark of the trunk and produce a circular incision in the bark. 
     The incision it makes has a diameter of approximately 8 cm.