20 FUNGI. 



the stem, gives the best notion of the arrangement of the 

 parts, and their relation to the whole. By this means it will be 

 seen that the pileus is continuous with the stem, that the sub- 

 stance of the pileus descends into the gills, and that relatively 

 the substance of the stem is more fibrous than that of the pileus. 

 In the common mushroom the ring is very distinct surrounding 

 the stem, a little above the middle, like a collar. In some 

 Agarics the ring is very fugacious, or absent altogether. The 

 form of the gills, their mode of attachment to the stem, their 

 colour, and more especially the colour of the spores, are all very 

 important features to be attended to in the discrimination of 

 species, since they vary in different species. The whole 

 substance of the Agaric is cellular. A longitudinal slice from 

 the stem will exhibit under the microscope delicate tubular 

 cells, the general direction of which is lengthwise, with lateral 

 branches, the whole interlacing so intimately that it is diffi- 

 cult to trace any individual thread very far in its course. It 

 will be evident that the structure is less compact as it approaches 

 the centre of the stem, which in many species is hollow. The 

 liymenium is the spore-bearing surface, which is exposed or naked, 

 and spread over the gills. These plates are covered on all sides 

 with a delicate membrane, upon which the reproductive organs 

 are developed. If it were possible to remove this membrane in 

 one entire piece and spread it out fiat, it would cover an 

 immense surface, as compared with the size of the pileus, for it 

 is plaited or folded like a lady's fan over the whole of the gill- 

 plates, or lamellee, of the fungus.* If the stem of a mushroom 

 be cut off close to the gills, and the cap laid upon a sheet of 

 paper, with the gills downwards, and left there for a few hours, 

 when removed a number of dark radiating line swill be deposited 

 upon the paper, each line corresponding with the interstices 

 between one pair of gills. These lines are made up of spores 

 which have fallen from the hymenium, and, if placed under the 

 microscope, their character will at once be made evident. If 

 a fragment of the hymenium be also submitted to a similar 

 examination, it will be found that the whole surface is studded 

 * In Paxillus involutus the hymenium may be readily torn off and unfolded. 



