FIG. 147. Psalliota campestris (cultivated form). Cross-section of part of a living gill showing semi- 

 diagrammatically the structure of the hymenium h, the subhymenium 8, and part of the trama t. 

 The gill is supposed to have been taken from a mushroom which has been shedding spores for about 

 24 hours and the hymenium of which will therefore not be totally exhausted for several days. A 

 dark area of the hymenial surface is passed through proceeding to the right from element no. 8 

 to element no. 34, a light area from element no. 34 to element no. 59, an intermediate area from 

 element no. 59 to element no. 63, and another intermediate area from element no. 1 to element no. 8. 

 As shown by the shading, in the light area the spores are unpigmented, in the intermediate areas 

 partially pigmented, and in the dark area fully pigmented. 



The elements of the hymenium can be analysed as follows : past -generations basidia, nos. 13, 

 21, 30, 38, and 51 ; present-generation basidia, nos. 3, 5, 11, 16, 24, 32, 41, 44, 48, 53, 57, and 61 ; 

 coming-generation basidia, nos. 8, 18, 28, 36, 42, 46, 55, and 60 ; future-generations basidia, nos. 2, 

 6, 7, 9, 12, 14, 17, 19, 23, 27, 29, 31, 34, 37, 45, 49, 52, 54, 59, and 62 ; paraphyses (permanently 

 sterile elements which enlarge as the hymenium becomes more and more exhausted), nos. 1, 4, 10, 

 15, 20, 22, 25, 26, 33, 35, 39, 40, 43, 47, 50, 56, 58, and 63. 



Parts of three waves of development are shown proceeding across the section from right to left. 

 The rear end (about three-ninths) of the foremost wave consists of the series of basidia, nos. 51, 

 38, 32, 24, 16, 11, 5, and 3. The middle part (about four-ninths) of the next succeeding wave consists 

 of the series of basidia nos. 61, 57, 53, 48, 44, 41, 36, 28, 18, and 8. The forepart (about two- 

 ninths) of the third wave which succeeds the second, consists of the series of basidia nos. 60, 55, 46, 

 42, and 34. There is a difference of about eight and one-half hours between each basidium of 

 one wave and its nearest neighbour of the preceding wave. Thus after eight and one -half hours 

 the basidium no. 8 will approximately resemble no. 5 as it is now, no. 18 will resemble no. 16, no. 28 

 will resemble no. 24, etc. 



The basidia of the rear part of the first wave will now be described. No. 51 has been in the 

 collapsed condition for an hour or more ; its concave end, drawn down to the general level of the 

 hymenium, conceals the sterigmatic stumps. No. 38 is in the act of sudden collapse about twenty 

 minutes after the discharge of its last spore ; its end is rapidly becoming concave, and its sterigmata 

 are being drawn into the concavity. No. 32 bears a spore which has a drop about ten seconds 

 old and of the maximum size on its hilum and which therefore should be shot away at once. The 

 other spore was shot away from its sterigma about a minute ago, in the direction indicated by the 

 arrow, to a distance of about 1 mm. This spore is shown in its flight with the water-drop attached 

 to it. No. 24 is about to shoot away its spores, for a water-drop is being rapidly excreted at 

 each spore-hilum. The right-hand drop is about eight seconds old and of nearly maximum size 

 which indicates that the spore to which it is attached should be shot away after the lapse of 

 about two more seconds. The other drop is only about two seconds old and therefore will con- 

 tinue to grow for about eight more seconds. The spores on both no. 32 and no. 24 are about 

 eight hours old. No. 16 bears fully pigmented spores which we may suppose to be six and one- 

 half hours old and therefore an hour and a half from the moment of spore-discharge. No. 11 also 

 has fully pigmented spores. These we may suppose to be five and a half hours old and therefore 

 two and a half hours from the moment of spore-discharge. Nos. 5 and 3 may be supposed to have 

 begun their development at the same moment. Their spores are becoming strongly pigmented, 

 and we may conclude that they are about four hours old and four hours from discharge. 



The basidia of the middle part of the second wave will now be described. No. 61 bears 

 spores which are becoming pigmented. We may suppose them to be three and a half hours old. 

 No. 57 bears a single sterigma and a spore of full size but unpigmented. We may suppose the 

 spore to be two hours old. No. 53 bears two spores of full size but unpigmented. We may suppose 

 them to be one hour old, so that they attained full size only twenty minutes ago. Nos. 48 and 

 44 bear spores which are far below full size and about ten minutes old. The spores of no. 41 are 

 only five minutes old. No. 36 bears full-grown sterigmata but no spores as yet. It resembles in 

 outward form a basidium which has just shot away its second spore, i.e. such a basidium as 

 no. 32 will be like within two seconds when the left-hand spore has been discharged, but differs 

 from it in being stuffed with contents instead of having its interior occupied by a large vacuole. 

 No. 28 bears sterigmata about two-thirds developed and no. 18 sterigmata about one-third developed. 

 No. 8 shows as yet not a trace of sterigmata. 



The basidia of the forepart of the third wave will now be described. No. 60 is almost, if not 

 quite, of full length. No. 55 has certainly not yet attained its full length, for it is not yet fully 

 protuberant. Nos. 46 and 42 are progressively younger and less protuberant. No. 34, which 

 forms the foremost element of the wave, is simply a future -generation basidium which does not 

 yet protrude beyond the general level of the hymenium. 



Most of the present -generation basidia are bisporous, but nos. 48 and 57 are monosporous. 

 The spore on no. 57 has about twice the volume of any spore on a bisporous basidium. Nos. 3 

 and 5 show the typical arrangement of the spores on any two very closely adjacent basidia which 

 happen to develop their spores simultaneously : the four spores are situated at the four corners of 

 a square or rectangle. Two waste spores, w w, are shown lying on the hymenium ; the basidia to 

 which they belonged failed to discharge them and they were therefore dragged down on to the 

 hymenium when these basidia collapsed. We may suppose that the basidium no. 51 shot away one 

 of its spores successfully but not the other ; hence the waste spore adjacent to its free end. 



The subhymenium s consists of several layers of rounded or oval cells. There is no sharply 

 defined level plane separating the hymenium from the subhymenium. The older basidia (the first 

 to develop spores) arise very deeply in the subhymenium, e.g. nos. 30 and 51 ; but nos. 5, 11, 13, 

 and 38 are also noteworthy in this respect. The basidia which successively come to maturity during 

 the several days of spore-discharge arise more and more toward the top of the hymenium and have 

 shorter and shorter bodies. The trama t consists of elongated cells forming irregularly anastomosing 

 chains which tend to run in a direction parallel to the median line of the cross-section of the gill. 

 Magnification, 1,060. The scale is divided into hundredths of a mm. 



