- Email: [email protected]
The spore deposit of Daldinia
[ 37 8 ] Trans. Brit. mycol. Soc. 39 (3), 378-380 (1956).
THE SPORE DEPOSIT OF DALDINIA By C. T. INGOLD Birkbeck College, University of London (With Plate 14) If a thick median slice is cut from an active stroma of Daldinia concentrica and laid horizontally on a glass plate, a spore deposit collects overnight as a black band about 1'0 em. wide and separated from the edge of the stroma by a more or less spore-free region 0'2-{)'3 em. wide. Further the spore deposit is zoned with several darker regions parallel with the surface of the stroma alternating with paler zones. It is suggested that both the considerable width of the deposit and its zoning are associated with the discharge of projectiles ranging from single spores to groups of eight.
If an active stroma of Daldinia concentrica, which is approximately hemispherical, is placed on a sheet of glass, covered to eliminate draughts and left overnight, there accumulates around it a spore deposit in the form of a black band extending outwards to a distance of about 1'2 em. from the edge of the stroma. The only information that this gives is that the maximum distance of discharge is about 1'2 em. In some recent experiments spore deposits were obtained not from whole stromata but from semicircular median vertical slices o- 5-0' 7 em. thick. Each slice was placed flat on a clean horizontal glass plate and left overnight. A typical spore-deposit obtained in this way is shown in PI. 14a. It will be seen first that the deposit does not take the form of a line parallel with the surface, but is a broad band 0'2-0'3 em. away from the surface and about 1'0 em. wide, and secondly that the deposit shows concentric zoning. This paper is concerned with an explanation of these two phenomena. Since all the neck canals of the perithecia immersed in the stroma are more or less at right angles to the surface, it is to be expected that the asci which protrude through the ostioles will discharge their spores roughly in this direction. If all the spore projectiles were of the same size and if all the asci burst with the same force one might suppose that the spore deposit would consist essentially of a line parallel with the edge of the stroma. However, because of variation in the force of ascus discharge and in the size of the ascospores some blurring of the line would be expected, but not to the extent of producing a wide band. The probable explanation becomes apparent when a spore deposit is examined microscopically. For this purpose an overnight accumulation is too dense and it is best to look at one which has been formed at night during the course of about half an hour. It is then seen that there are many single ascospores in the deposit, and also groups ranging from two
Daldinia spore deposit. C. T. Ingold
379
to eight; single spores, and groups of eight being, perhaps, the commonest.* We see then that the ascospore projectiles from a discharging Daldinia consist normally offrom one to eight spores. It is very unusual to find an ascus with less than eight spores, so where a projectile consists of fewer than eight it has probably been formed from part only of the ascus contents, or, in other words, the contents have become separated into more than one projectile and, indeed, often eight are formed. No doubt there is a break-up of the spore jet so that droplets containing less than eight spores are formed. With microscopic spherical projectiles the distance (d) of discharge with a given initial velocity is expressed by d = Kr 2 , where r is the radius of the projectile and K a constant. We would expect, therefore, that 8-spored projectiles would be shot farther than those consisting of a single spore. This is easily confirmed by looking at the spore deposit. On the outer boundary only groups (mostly 8-spored) are to be seen, whilst on the inner boundary there are great numbers of single spores, although a few groups of spores of the other sizes are also present (PI. 14b, c). We may suppose that there are eight possible spore projectiles with volumes I, 2, 3, 4, 5, 6, 7 and 8, neglecting the fluid associated with the spores or assuming that the amount is proportional to the number of spores present. If we assume that these projectiles are spherical, which is not in fact so but may not be very far from the truth, then the relative distances of discharge with a given initial velocity are determined by the squares of the cube roots of the numbers namely: 1'00, 1'59, 2'08, 2'52, 2'92, 3'30, 3.66 and 4'00. The result would be a broad band of spores parallel with the surface of the stroma and at a certain distance from it, and if this distance is one unit then the band will have a breadth of three units. This is, in fact, very much the picture that is actually obtained, the white zone between the stroma and the deposit being about a third, or perhaps a quarter, of the width of the deposit itself. Now if each of the eight sizes of projectile were discharged to its now characteristic distance, the deposit would have eight concentric zones, the outer ones becoming progressively closer together. In fact the deposit is usually zoned but the sharpness of the zoning varies considerably. Further the number of dark zones is always less than eight-usually only three or four. Nevertheless, it seems likely that the phenomenon of zoning is due to the occurrence of projectiles of a limited number of sizes with some of the zones tending to run together. Very probably some sizes of projectile are commoner than others so that certain zones may be emphasized at the
* There are also occasional clumps each composed of a large number of spores. These seem to arise in the following manner. Spore tendrils may occur in Daldinia. When this happens an ascus ruptures at the ostiole and its contents, instead of being violently discharged, simply ooze out. The next ascus follows suit adding its eight spores below the first eight, and if this goes on repeatedly, a spore tendril several millimetres long may be produced. Sometimes, shortly after a tendril has begun to form, an ascus succeeds in exploding with sufficient force not only to discharge its own eight spores, but also to carry away with them the accumulated spore mass of the incipient tendril. Such masses are normally shot only a very short distance-rarely more than a millimetre or two.
380
Transactions British Mycological Society
expense of others. Again the distance to which spore projectiles of each size are shot will certainly vary about a mean position and with the shorter range the smaller projectiles might be expected to show less absolute amplitude of variation than the larger ones with the greater range. Thus the inner zones would be expected to be more clearly defined and the outer ones more blurred. EXPLANATION OF PLATE 14
a: spore deposit accumulated overnight around a thick median slice of Daldinia concentrica. b, c: photographs taken under low power of the inner edge (b) and the outer edge (c) of a thin spore deposit, obtained after about half an hour, from a thick slice of Daldinia.
(Accepted for publication 28 September 1955)
Trans. Brit. Myc. Soc.
Vol. 39. Plate 14
(Facing p. 380)
THE SPORE DEPOSIT OF DALDINIA By C. T. INGOLD Birkbeck College, University of London (With Plate 14) If a thick median slice is cut from an active stroma of Daldinia concentrica and laid horizontally on a glass plate, a spore deposit collects overnight as a black band about 1'0 em. wide and separated from the edge of the stroma by a more or less spore-free region 0'2-{)'3 em. wide. Further the spore deposit is zoned with several darker regions parallel with the surface of the stroma alternating with paler zones. It is suggested that both the considerable width of the deposit and its zoning are associated with the discharge of projectiles ranging from single spores to groups of eight.
If an active stroma of Daldinia concentrica, which is approximately hemispherical, is placed on a sheet of glass, covered to eliminate draughts and left overnight, there accumulates around it a spore deposit in the form of a black band extending outwards to a distance of about 1'2 em. from the edge of the stroma. The only information that this gives is that the maximum distance of discharge is about 1'2 em. In some recent experiments spore deposits were obtained not from whole stromata but from semicircular median vertical slices o- 5-0' 7 em. thick. Each slice was placed flat on a clean horizontal glass plate and left overnight. A typical spore-deposit obtained in this way is shown in PI. 14a. It will be seen first that the deposit does not take the form of a line parallel with the surface, but is a broad band 0'2-0'3 em. away from the surface and about 1'0 em. wide, and secondly that the deposit shows concentric zoning. This paper is concerned with an explanation of these two phenomena. Since all the neck canals of the perithecia immersed in the stroma are more or less at right angles to the surface, it is to be expected that the asci which protrude through the ostioles will discharge their spores roughly in this direction. If all the spore projectiles were of the same size and if all the asci burst with the same force one might suppose that the spore deposit would consist essentially of a line parallel with the edge of the stroma. However, because of variation in the force of ascus discharge and in the size of the ascospores some blurring of the line would be expected, but not to the extent of producing a wide band. The probable explanation becomes apparent when a spore deposit is examined microscopically. For this purpose an overnight accumulation is too dense and it is best to look at one which has been formed at night during the course of about half an hour. It is then seen that there are many single ascospores in the deposit, and also groups ranging from two
Daldinia spore deposit. C. T. Ingold
379
to eight; single spores, and groups of eight being, perhaps, the commonest.* We see then that the ascospore projectiles from a discharging Daldinia consist normally offrom one to eight spores. It is very unusual to find an ascus with less than eight spores, so where a projectile consists of fewer than eight it has probably been formed from part only of the ascus contents, or, in other words, the contents have become separated into more than one projectile and, indeed, often eight are formed. No doubt there is a break-up of the spore jet so that droplets containing less than eight spores are formed. With microscopic spherical projectiles the distance (d) of discharge with a given initial velocity is expressed by d = Kr 2 , where r is the radius of the projectile and K a constant. We would expect, therefore, that 8-spored projectiles would be shot farther than those consisting of a single spore. This is easily confirmed by looking at the spore deposit. On the outer boundary only groups (mostly 8-spored) are to be seen, whilst on the inner boundary there are great numbers of single spores, although a few groups of spores of the other sizes are also present (PI. 14b, c). We may suppose that there are eight possible spore projectiles with volumes I, 2, 3, 4, 5, 6, 7 and 8, neglecting the fluid associated with the spores or assuming that the amount is proportional to the number of spores present. If we assume that these projectiles are spherical, which is not in fact so but may not be very far from the truth, then the relative distances of discharge with a given initial velocity are determined by the squares of the cube roots of the numbers namely: 1'00, 1'59, 2'08, 2'52, 2'92, 3'30, 3.66 and 4'00. The result would be a broad band of spores parallel with the surface of the stroma and at a certain distance from it, and if this distance is one unit then the band will have a breadth of three units. This is, in fact, very much the picture that is actually obtained, the white zone between the stroma and the deposit being about a third, or perhaps a quarter, of the width of the deposit itself. Now if each of the eight sizes of projectile were discharged to its now characteristic distance, the deposit would have eight concentric zones, the outer ones becoming progressively closer together. In fact the deposit is usually zoned but the sharpness of the zoning varies considerably. Further the number of dark zones is always less than eight-usually only three or four. Nevertheless, it seems likely that the phenomenon of zoning is due to the occurrence of projectiles of a limited number of sizes with some of the zones tending to run together. Very probably some sizes of projectile are commoner than others so that certain zones may be emphasized at the
* There are also occasional clumps each composed of a large number of spores. These seem to arise in the following manner. Spore tendrils may occur in Daldinia. When this happens an ascus ruptures at the ostiole and its contents, instead of being violently discharged, simply ooze out. The next ascus follows suit adding its eight spores below the first eight, and if this goes on repeatedly, a spore tendril several millimetres long may be produced. Sometimes, shortly after a tendril has begun to form, an ascus succeeds in exploding with sufficient force not only to discharge its own eight spores, but also to carry away with them the accumulated spore mass of the incipient tendril. Such masses are normally shot only a very short distance-rarely more than a millimetre or two.
380
Transactions British Mycological Society
expense of others. Again the distance to which spore projectiles of each size are shot will certainly vary about a mean position and with the shorter range the smaller projectiles might be expected to show less absolute amplitude of variation than the larger ones with the greater range. Thus the inner zones would be expected to be more clearly defined and the outer ones more blurred. EXPLANATION OF PLATE 14
a: spore deposit accumulated overnight around a thick median slice of Daldinia concentrica. b, c: photographs taken under low power of the inner edge (b) and the outer edge (c) of a thin spore deposit, obtained after about half an hour, from a thick slice of Daldinia.
(Accepted for publication 28 September 1955)
Trans. Brit. Myc. Soc.
Vol. 39. Plate 14
(Facing p. 380)