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On the production of imperfectly developed spores in the Agaricaceae
O N T H E P R O D U C T I 0 , N O F IMPERFECTLY DEVELOPED SPORES IN T H E AGARICACEAE.
By A. D. Cotton, F.L.S. In practically all groups of Fungi except the Hymenomycetes, the size and shape of the spore is an important item in the diagnosis of the species. In the Hymenomycetes, however, specially in the Agaricaceae, the spore has never been given a prominent place. This is no doubt largely due to the fact that most species possess good field characters, and being in the main macroscopic plants, resource to the microscope is unnecessary. But there is an idea prevalent (which to a certain extent is supported by the literature) that the spores vary more in this group than in others, and, that for this reason, they are almost useless for systematic purposes. It is true that in certain genera they are of little value (for the reason that they are practically uniform in all the species), but in others they afford a most useful supplementary character, and there is no evidence whatever to show that these bodies, so valuable in other groups of fungi, are less constant in the Agaricaceae. The ordinary precautions necessary when examining external morphological characters are just as needful when microscopic features are in question. As pointed out on p. 231, care must be exercised to select good average spores, and also those that have reached maturity. In addition, it is important to remember the possible existence of characteristic variability, i.e., that variability may be a feature characteristic of the species in question. The presence of ill-nourished spores was also alluded to. It appears unlikely that such spores are frequent in nature, but under certain artificial conditions, a whole crop may be produced which if not recognised as abnormal would convey a totally wrong impression. Since no account of spores of this type has, as far as I know, been published, the following details may be of interest. The point came to light last season during an examination of Falkland Island material ;elf Stropharia semiglobata. The question was raised as to wheLher the first shed spores from a given pileus differed at all from those which were liberated later. T o determine this a succession of spore-casts was prepared from English specimens. Vigorous young sporophores of S. semiglobata were used, and the pilei set on white paper in the ordin-
ary way, covered with small glasses, and shifted every .hour to a fresh position. The experiments were carried out in the Kew Herbarium and during the summer months, that is, in a fairly dry warm atmosphere. The spores fell copiously during the first day, and also during the night. By the morning the pilei were somewhat shrivelled, but a series of spore-casts was obtained during the second day, shifting being done in this case about every two hours. During the second night spores continued to fall, but by the morning the majority of the pilei had dried up too much to be of further use. Microscopic examination of the spores gave a rather startling result. Whilst those of the first day p were a deep purple black, those demeasured I 8-20 x 9- ~ o and posited on the morning of the third day were not more than twothirds of the original size and much paler in colour. The intervening spore-casts showed a gradual diminution in size, though this was not noticeable during the first few hours. The figures for one example were as under, the average measurement, as nearly as possible, of the spores being calculated. 36th hour ...... 14 x 8p 1st hour ...... 18 x ~ o p 13th hour ... 1 6 x gp 48th hour ...... 1 3 x 8 ~ ~ 3 r dhour ... I 5 x gp 83rd hour ...... 12 x 7P This experiment was repeated several times, and always gave similar results though the reduction in spore-size was not quite so great in most cases. Other species were tried, but as none had such large spores the results were not so striking, nor did the plants in all cases behave in quite the same way. At first these observations seemed to show that the last shed spores differed decidedly from the earliest and to afford an explanation of the discrepancies in handbooks, and even to provide an argument against their use. But further examination proved that the results obtained were artificial, and that in practice the danger is more apparent than real. It was found that when plants of S. semiglobata grown under natural conditions were examined, old specimens showed spores that were of normal size, and in no case was there a crop of small spores. The explanation lies doubtless in the fact, that in the first case the pilei were separated from the stalk, and the experiments performed in a dry warm atmosphere; under these conditions spores continue to develop for two or three days, but are poorly nourished, and fall off without reaching the normal size. This conclusion was confirmed by the following little experiment. Whole sporophores (pileus, stalk, and base) were collected and placed upright in large test tubes, supplied with a little water and stood out of doors in a damp shady position. In order to obtain spore-casts, each sporophore had a paper collar fixed beneath the gills. The plant could easily be taken out of the tubes by means of curved forceps, and the collars, which were changed daily, were
placed in position and removed by means of a lateral slit. Under the conditions of this experiment spores continued to fall for several days, usually five or six, occasionally eight, or even nine. An examination of the collars showed practically no difference in the size of the spores. After the fifth or sixth day the spores were few and slightly paler in colour, but the majority reached thk normal dimensions, though several fell short. These observations, together with the examination of many old specimens, justify us in saying that the spores formed on the gill of S. semiglobata are practically uniform in size throughout the whole life of the plant. As there is no evidence which leads us to expect that this species differs from other Agarics, we may fairly infer that the above conclusion holds good generally, and that, as long as mature spores are examined, the exact age of the specimen is not of great importance. No conditions comparable with the severance of the pileus from the stipe occur in nature (very rapid desiccation being perhaps the nearest to it), hence, though a few ill grown spores will be found on almost every naturally grown specimen, the production of a crop of such spores is probably unknown.
By A. D. Cotton, F.L.S. In practically all groups of Fungi except the Hymenomycetes, the size and shape of the spore is an important item in the diagnosis of the species. In the Hymenomycetes, however, specially in the Agaricaceae, the spore has never been given a prominent place. This is no doubt largely due to the fact that most species possess good field characters, and being in the main macroscopic plants, resource to the microscope is unnecessary. But there is an idea prevalent (which to a certain extent is supported by the literature) that the spores vary more in this group than in others, and, that for this reason, they are almost useless for systematic purposes. It is true that in certain genera they are of little value (for the reason that they are practically uniform in all the species), but in others they afford a most useful supplementary character, and there is no evidence whatever to show that these bodies, so valuable in other groups of fungi, are less constant in the Agaricaceae. The ordinary precautions necessary when examining external morphological characters are just as needful when microscopic features are in question. As pointed out on p. 231, care must be exercised to select good average spores, and also those that have reached maturity. In addition, it is important to remember the possible existence of characteristic variability, i.e., that variability may be a feature characteristic of the species in question. The presence of ill-nourished spores was also alluded to. It appears unlikely that such spores are frequent in nature, but under certain artificial conditions, a whole crop may be produced which if not recognised as abnormal would convey a totally wrong impression. Since no account of spores of this type has, as far as I know, been published, the following details may be of interest. The point came to light last season during an examination of Falkland Island material ;elf Stropharia semiglobata. The question was raised as to wheLher the first shed spores from a given pileus differed at all from those which were liberated later. T o determine this a succession of spore-casts was prepared from English specimens. Vigorous young sporophores of S. semiglobata were used, and the pilei set on white paper in the ordin-
ary way, covered with small glasses, and shifted every .hour to a fresh position. The experiments were carried out in the Kew Herbarium and during the summer months, that is, in a fairly dry warm atmosphere. The spores fell copiously during the first day, and also during the night. By the morning the pilei were somewhat shrivelled, but a series of spore-casts was obtained during the second day, shifting being done in this case about every two hours. During the second night spores continued to fall, but by the morning the majority of the pilei had dried up too much to be of further use. Microscopic examination of the spores gave a rather startling result. Whilst those of the first day p were a deep purple black, those demeasured I 8-20 x 9- ~ o and posited on the morning of the third day were not more than twothirds of the original size and much paler in colour. The intervening spore-casts showed a gradual diminution in size, though this was not noticeable during the first few hours. The figures for one example were as under, the average measurement, as nearly as possible, of the spores being calculated. 36th hour ...... 14 x 8p 1st hour ...... 18 x ~ o p 13th hour ... 1 6 x gp 48th hour ...... 1 3 x 8 ~ ~ 3 r dhour ... I 5 x gp 83rd hour ...... 12 x 7P This experiment was repeated several times, and always gave similar results though the reduction in spore-size was not quite so great in most cases. Other species were tried, but as none had such large spores the results were not so striking, nor did the plants in all cases behave in quite the same way. At first these observations seemed to show that the last shed spores differed decidedly from the earliest and to afford an explanation of the discrepancies in handbooks, and even to provide an argument against their use. But further examination proved that the results obtained were artificial, and that in practice the danger is more apparent than real. It was found that when plants of S. semiglobata grown under natural conditions were examined, old specimens showed spores that were of normal size, and in no case was there a crop of small spores. The explanation lies doubtless in the fact, that in the first case the pilei were separated from the stalk, and the experiments performed in a dry warm atmosphere; under these conditions spores continue to develop for two or three days, but are poorly nourished, and fall off without reaching the normal size. This conclusion was confirmed by the following little experiment. Whole sporophores (pileus, stalk, and base) were collected and placed upright in large test tubes, supplied with a little water and stood out of doors in a damp shady position. In order to obtain spore-casts, each sporophore had a paper collar fixed beneath the gills. The plant could easily be taken out of the tubes by means of curved forceps, and the collars, which were changed daily, were
placed in position and removed by means of a lateral slit. Under the conditions of this experiment spores continued to fall for several days, usually five or six, occasionally eight, or even nine. An examination of the collars showed practically no difference in the size of the spores. After the fifth or sixth day the spores were few and slightly paler in colour, but the majority reached thk normal dimensions, though several fell short. These observations, together with the examination of many old specimens, justify us in saying that the spores formed on the gill of S. semiglobata are practically uniform in size throughout the whole life of the plant. As there is no evidence which leads us to expect that this species differs from other Agarics, we may fairly infer that the above conclusion holds good generally, and that, as long as mature spores are examined, the exact age of the specimen is not of great importance. No conditions comparable with the severance of the pileus from the stipe occur in nature (very rapid desiccation being perhaps the nearest to it), hence, though a few ill grown spores will be found on almost every naturally grown specimen, the production of a crop of such spores is probably unknown.