AGARICUS 229 



periphery, and that throughout, intercellular spaces are to be 

 recognized. 



VII. Passing to the pileus of the mature mushroom, cut 

 tangential vertical sections through it in such a way as to tra- 

 verse the vertical gills at right angles to their surface : great 

 care must be taken that the surfaces of the gills shall not be 

 injured in the process of preparation, otherwise the basidia and 

 spores which project from their surfaces cannot be observed. 

 Mount in glycerine and examine under a low power : the chief 

 bulk of the section will consist of the massive tissues of the 

 pileus, which show little or no differentiation ; passing down- 

 wards to the lower surface where the gills or lamellae have been 

 traversed, the sections of these will be seen as fringe-like pro- 

 jections from the lower surface : occasionally branching of the 

 gill may be recognized. 



Examine the sections in detail under a high power : the 

 following observations are to be made 



1. The mass of tissue of the pileus consists of a plexus of 

 much-branched hyphse, with large intervening spaces : it is 

 composed of short cells, similar in their characteristics to those 

 which compose the stipe : the chief difference lies in their 

 arrangement. This spongy tissue becomes denser about the 

 insertion of the lamellae. 



2. The sections through the lamellae show a differentiation 

 into 



a. The central portion (trama), in which the septate hyphal 

 filaments are easily recognized running longitudinally down the 

 middle of each lamella, and curving outwards at their ends 

 towards the free surface. 



b. The sub-hymeniai layer, composed of shorter, closely- 

 packed cells, constituting a pseudo-parenchyma : this consists 

 of the short-celled, terminal parts of the hyphal filaments which 

 compose the trama. 



c. The hymenial layer, consisting of oblong, closely packed 

 cells, having their longer axes perpendicular to the outer 

 surface : of these cells two types are to be distinguished 



i. The paraphyses, which are somewhat narrower and 

 have smooth rounded ends. 



