The invention relates to a noise-reducing track cover. The invention has particular, although not exclusive, application to railway tracks. Cover elements for reducing noise of tracks may have 5 the form of troughs which are set up at the track by means of a larger number of supporting elements and carrying elements. This results in relatively high structural expenditures and complex manipulations. Also other track covers are formed with cover 10 elements comprised at least on their upper side of a slab shaped, sound absorbing material. Sound absorbing materials as a rule are mechanically sensitive, mostly porous and also have relatively high production costs, and require great care when being installed in track systems. is These properties do not agree with the conditions generally prevailing in track systems. By pressure loads exerted by walking over such cover elements of sound absorbing design and by the impact caused by the falling of various objects on the cover elements, the latter are 20 easily damaged. Moreover, in the area of railway facilities, undesired deposits of fine, particulate material form easily, and such deposits may cause a negative change in the noise-dampening capacity achieved by sound-absorbing apertures or pores of cover elements. 25 It is an object of the present invention to provide a noise-reducing track cover of the initially defined type, in which the disadvantages of the aforementioned type are largely avoided. Advantageously the track covers can be produced with 30 relatively little expenditures in terms of construction and of mounting technique. Additionally with the mounting technique, it is desirable to have a stable fit of the cover elements on the track under the rough conditions of the railroad operation. By the installation of the cover 35 elements, it is advantageous for the dynamic behaviour of the track to be changed as little as possible. The track cover, therefore is characterised in that 2298289_1 (GHMatters) 28/06/10 -2 cover elements arranged between the rails of the track are provided, which cover elements have supporting noses at their rims that face the rails which supporting noses engage in the lateral recesses of the rails with elastomer 5 sections interposed, and said cover elements are supported merely on the rails by means of these supporting noses and self-supportingly bridge the space between the rails from rail to rail. The cover elements have a slab-like base and, on their upper side, a layer of loose particles for 10 plants to take root therein. In such track covers, by providing the layer for plants to take root therein on the cover elements, a dense growth of plants filling the entire area can be obtained, and it has been shown that cover elements provided with a 15 plant growth in this manner have good sound-absorbing properties. Such a plant growth is relatively simple to obtain by sowing or by planting or, under favourable conditions, may even form by itself. By this design, the aforementioned objects can well 20 be met. The supporting of the cover elements by means of the supporting noses provided on these cover elements, which supporting noses engage in the lateral recesses of the rails, there results a very stable fit of the cover elements in a structurally simple manner, installation of 25 the cover elements in the track and a possible removal of the former for the purpose of maintenance work being easy to accomplish. The self-supporting bridging of the space present between the rails of the respective track avoids a detrimental influence on the track bedding by the cover 30 elements, and in this manner a detrimental influence on the dynamic behaviour of the track is prevented. Moreover, by the fact that the cover elements are supported merely on the rails, the noise dampening effect obtained by the plants growing on the cover elements can 35 be further improved. A preferred embodiment of the track cover according 22982891 (GHMatters) 28/06/10 -2A to the invention is characterised in that cover elements arranged to externally adjoining the rails are provided, which cover elements have supporting noses on their rim that faces the respective rail, said supporting noses 5 engaging in the lateral recesses of the respective rails with elastomer sections interposed, said cover elements being supported on the respective rail merely by these supporting noses and, on their side facing away from this rail, are supported on a pedestal provided adjacent the 10 track and self-supportingly bridge the space between the respective rail and the pedestal. Furthermore, it is very suitable if it is provided for the layer provided for plants to take root therein to be covered by a non-woven fabric. By this measure, both is the layer provided for plants to take root therein and also the plants that are rooted in this layer and which penetrate the non-woven fabric, can be 22982891 (GHMatters) 2806/10 -3 protected in a simple manner, and in particular, it can be achieved that the material of the layer provided for plants to take roots therein as well as the plants rooted in this layer are protected against the suction action exerted by rapidly mov ing rail-borne vehicles, and moreover, it is ensured in this manner that already shortly after the layer provided for plants to take roots therein has been applied, the cover elements can be walked on or light vehicles, e.g. lawn mowers, can be moved thereon without any negative effects. For this purpose it is also provided for the slab-like base of the cover elements to have a sufficient dimensional stability at least for walking thereon and for movement thereon with light equipment. In order to prevent undesired accumulations of rain water or of other liquids on the cover elements, it is advantageous to provide the cover elements with drain openings and/or drain channels. An embodiment of the cover elements of very simple construc tion which also is easy to handle during installation in the track and during a possible removal from the track is character ised in that the slab-like base of the cover elements has the shape of a U-section extending transversely to the rail-longit udinal direction, which U-section is formed of a substantially plane bottom plate and of flange ribs projecting upwards from the bottom plate and provided at those rims of the bottom plate which extend transversely to the rail longitudinal direction, the rail-side supporting of the cover elements being effected by supporting noses which are formed by the ends of the flange ribs that face the rails. A further embodiment of the inventive track cover which, above all, is advantageous as regards its handling during in stallation of the cover elements in the track and during a pos sible removal of the cover elements from the track is characterised in that the cover elements arranged between the rails of the track so as to extend from rail to rail are de signed in the form of partial cover element forming element pairs, the partial cover elements of each pair being assembled in hinge-like manner and the geometric hinge axis extending in parallel to the rails. In this embodiment, it is further advant ageous if it is provided that the partial cover elements of each element pair are supported on each other at their rims which -4 face each other, and with each partial cover element, along its rim that faces the other partial cover element of the respective pair, carrying sections and resting sections are provided in me ander-like alternating succession, the resting sections of the one partial cover element of the respective pair resting on the carrying sections of the other partial cover element, and the resting sections of the other partial cover element of the re spective pair resting on the carrying sections of the one par tial cover element. The invention will now be described in more detail herein after and with reference to the drawing in which exemplary em bodiments of the subject matter of the invention are schematically illustrated. In the drawings, Fig. 1 shows a track provided with a first embodiment of an inventively designed track cover, in a section made transversely to the longitudinal direction of the track; Fig. 2 shows a variant to the former, in which the base of the cover elements has a depressed upper side, in a section analogous to that of Fig. 1; Fig. 3 shows an embod iment in which the base of the cover elements has the shape of a trough, once more in a section extending transversely to the longitudinal direction of the track; Fig. 4 shows an embodiment, in which the base of the cover elements has the shape of a U section, in a section extending transversely to the longitudinal direction of the track, and Fig. 5 shows this embodiment in a section extending in the longitudinal direction of the track, according to line V-V of Fig. 4; Fig. 6 shows an embodiment in which the cover elements of the track cover are designed in the form of partial cover elements assembled in pairs, in a section extending transversely to the longitudinal direction of the track, and Fig. 7 shows this embodiment in an axonometric view in the folded-up state, as results during the installation or removal of the cover elements. In the track 1 illustrated in Fig. 1, the rails 2, 2' of the track are fastened to sleepers 4 by means of rail fastening ele ments 3, the sleepers 4 in turn being carried on a bed of gravel 5. This track is provided with an embodiment of a track cover designed according to the invention, which is formed with cover elements 6 arranged between the rails 2, 2' and with cover ele ments 7 externally adjoining the rails 2, 2'. The cover elements 6, 7 have a slab-like base 8 and, on their upper side 9, a layer -5 10 provided for plants to take root therein. Plants 11 rooted in this layer 10, which may be grasses, e.g., are sketched. The slab-like base of the cover elements 6 has rim ledges 12 delim iting the layer 10 provided for plants to take root therein to wards the flange grooves 13; these rim ledges 12 may also be moulded to the base 8 or joined thereto. In analogous manner, rim ledges 12' are provided at the cover elements 7 delimiting the layer 10, provided at these cover elements for plants to take root therein, at the rims of the cover elements 7 that ex tend in the longitudinal direction of the rails. In order to meet the requirements of rail traffic, the grow ing plants can also be cut frequently, with appropriate ma chines, e.g., moving on the track. To form the layer provided for plants to take root therein, various materials may be used. Thus, in addition to soil, humus and sand, e.g., also granular materials, such as, e.g., clay or rock particles or plastics granules may be used, and also foamed material in plate or particle form. By means of the base of the cover elements, a clear-cut separation between this layer provided for plants to take root therein and the track bedding is given, and neither the plant growth nor the fine material, which forms the layer for the plants to take root therein, can negatively affect the track bedding. The material forming the layer for plants to take root therein can be applied to base parts of the cover elements that have already been laid, which simplifies the laying, since weight load resulting from the layer provided for plants to take root therein does not exist when laying the cover elements. By the continuous growth of the plants, a regeneration of the sound-absorbing properties is also given after disturbing influ ences. The rims 14 of the cover elements 6, 7 which face the rails 2, 2' have the shape of supporting noses 15 which are supported on the rails with elastomer sections 16 interposed. In this man ner, the cover elements 6 are mounted on the rails 2, 2' only and self-supportingly bridge the space 17 between the rails 2, 2' from rail to rail. At their side facing away from the re spective rail 2, 2', the cover elements 7 are supported on ped estals 18 located adjacent the track, with elastomer sections 19 interposed, there also existing a self-supporting bridging from the respective rail 2, 2' to the respective pedestal 18. In the -6 longitudinal direction of the track, a plurality of cover ele ments 6, 7 each is consecutively arranged. On the rims of the cover elements which extend transversely to the longitudinal direction of the track, rim ledges may be provided at the base 8 of the cover elements, which rim ledges will delimit the layer 10 provided for plants to take root therein at the individual cover elements, or a layer 10 that extends continuously over several cover elements may be provided, with the cover elements 6, 7 having to be laid in abutting sequence and any possibly re maining narrow gaps between successive cover elements having to be bridged with a cover strip or having to be closed with a joint filler. It is advantageous to arrange a non-woven fabric 20 on the layer 10 provided for plants to take root therein, since in this manner the layer 10 and also the plants 11 growing thereon will be stabilized against external influences. To drain off liquid substances which act on the cover elements - these influences also including rain water - drain openings 21 are provided at the base 8 of the cover elements 6, 7. The illustrated assembly of the track 1 on a bed of gravel 5 is to be seen as by way of example. Also other embodiments of the substructure are possible. In the variant of the Fig. 1-embodiment illustrated in Fig. 2, the only thing shown of the track cover is a cover element 6, arranged between the rails 2, 2' of the track. Of course, also with this variant, cover elements externally adjoining the rails 2, 2' of the track can be provided. The illustrated base 8 ex hibits depressions 22 on its upper side 9 which are separated by ribs 23 from each other. By this depressed configuration of the upper side 9 of the base 8 of the cover elements 6, a good hold of the layer 10, for plants to take root therein, on the base 8 is attained. Also in this variant shown in Fig. 2, drain open ings 21 are provided in the base 8. If desired, a non-woven fab ric may also be arranged on this layer 10 provided for plants 11 to take root therein. In the embodiment illustrated in Fig. 3, the base of the cover elements has the shape of a trough 25, and each one of these troughs 25 is filled with the layer 10 provided for plants 11 to take root therein. Supporting noses 15 are moulded to the rims 14 of the trough 25, which supporting noses are supported on the rails 2, 2' with elastomer sections 16 interposed, and in this manner, the cover elements 6 of the track cover are merely supported on the rails 2, 2' and self-supportingly bridge the space 17 between the rails from rail to rail. The troughs 25 are provided with drain openings 21. In the Figs. 4- and 5-embodiment of an inventively designed track cover, the slab-like base 8 of the cover elements 6 has the form of a U-section 27 extending transversely to the rail longitudinal direction. This U-section is formed of a substan tially plane bottom plate 28 and of flange ribs 29 which begin at those rims of the bottom plate 28 that extend transversely to the rail-longitudinal direction and which project upwards from the bottom plate 28. These cover elements 6 are carried by sup porting noses 30, with elastomer sections 16 interposed, on the rails 2, 2' only, and self-supportingly bridge the space 17 between the rails from rail to rail. The supporting noses 30 are merely formed by the ends of the flange ribs 29 facing the rails. The space present in the U-section 27 between the flange ribs 29 is filled with the layer 10 provided for plants 11 to take root therein. In this embodiment, drain channels 24 are provided to drain off liquid substances, which drain channels lead to drain openings 21 or may also directly lead to the out side. Such drain channels 24 may advantageously be shaped in a flow-promoting manner. In the embodiment illustrated in Figs. 6 and 7 of a track cover designed according to the invention, the cover elements arranged between the rails 2, 2' of the track have the form of partial cover elements 31, 31' which together form element pairs. The partial cover elements 31, 31' of each one of these pairs are assembled in hinge-like manner, the geometric hinge axis 32 extending in parallel with the rails 2, 2'. The partial cover elements 31, 31' of each element pair are supported on each other on their rims 33, 33' which face each other. In each partial cover element, along the rim that faces the other par tial element of the respective pair, carrying sections 34 or 34', respectively, and resting sections 35 or 35', respectively, are provided in meander-like alternating succession. The resting sections 35 of the one partial cover element 31 of the respect ive pair rest on the carrying sections 34' of the other partial carrying element 31' of the respective pair, and the resting -8 sections 35' of the other partial cover element 31' of the respective pair rest on the carrying sections 34 of the one partial cover element 31 of the respective pair. In this manner, the partial cover elements 31, 31' are 5 connected in pairs to a slab-like element which, in the levelled position, as illustrated in Fig. 6, is capable of carrying loads, these not only being loads derived from the layer 10 provided for plants to take roots therein and from those plants 11 that are rooted therein, but also io loads coming from the outside, as they occur when such a track cover is walked or driven over. In the case illustrated in Figs. 6 and 7, each base of the partial cover elements 31, 31' has the shape of a trough 36, and these troughs 36 are carried on the rails 2, 2' by means 15 of supporting noses 15 moulded to the rail-side rim of the respective trough, with elastomer sections 16 being interposed. The space 17 between the rails 2, 2' is self supportingly bridged from rail to rail. In Fig. 7, the growth formed by the plants 11 and extending over the 20 upper side of the partial cover elements has been outlined in the form of a geometric pattern for the sake of simplicity. By the possibility illustrated in Fig. 7 of folding up the partial cover elements of each pair in hinge-like manner, insertion of these cover elements into 25 the track and a possibly required removal of the cover elements from the track are substantially facilitated. For the sake of simplicity, in the embodiments of the track cover designed according to the invention and illustrated in Figs. 3 to 7, only the cover elements 30 arranged between the rails 2, 2' of a track have been illustrated. Yet, also with these embodiments, it is possible to provide cover elements externally adjoining the rails of the track. In the claims which follow and in the preceding 35 description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as 22982891 (GHMatters) 28/06/10 -9 "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 22982891 (GHMatters) 28/06/10