24 MASSACHUSETTS HORTICULTURAL SOCIETY. 



substance of which is made up of the compacted and closely inter- 

 woven threads and their branches. Along certain radiating lines is 

 formed the framework of the gills, which in the developed mush- 

 room is called the trania. Just below the gills an air space ap- 

 pears, the outer wall of which becomes the so-called veil. Lastly, 

 upon the surface of the gills develops a layer of cells standing 

 side by side like the single threads in the pile of velvet or in the 

 surface of an Oriental rug. 



With these cells we have a special concern. Taken together 

 they form the hymenium, the spore-producing tissue, which, 

 folded like a fan, is applied to both sides of the gill-plates. A 

 section through a gill shows us this layer. Each one of the club- 

 shaped spore-bearing cells composing it is called a f>asidinm. 

 Each basidium bears four spores on minute stalks. 



So far we have dealt exclusively with gill-bearing mushrooms, 

 a group to which as a whole is given the name Agaricixi. There 

 are other common kinds in which also basidia and spores are 

 developed on an exposed hy menial surface. The hymenium is dis- 

 posed in different ways. In one group, a large one, it lines the 

 inside of small tubes which are fastened vertically, with the open 

 mouths downward, in a closely packed mass on the under side 

 of the pileus ; this is the group of Polyporei. In a third group, 

 the Hydnei, it covers the surface of spines, teeth, or other 

 protuberances. In a fourth it is smooth, without distinctive 

 feature, evenly spread over one or both sides of the tough, or 

 coriaceous, thin body of the plant ; this is the character of the 

 Thelephorei. In a fifth group, the Clavariei, the plant i& 

 tender, fleshy, erect, and often densely branching, bearing the hy- 

 menium on all sides of the tips of the branches. Last are placed 

 the rather shapeless, gelatinous Tremellinei, which shrivel when 

 dry, and swell again with moisture ; in these the hymenium 

 covers the outer surface. From the similar nature of the hyme- 

 nium and its exposure in these six groups they are classed together 

 as the Hymejtomycetes. To this natural class, " vasta Fungorum 

 classis," as it was called by Fries, whose treatment of it still 

 remains the basis of later classifications, belong most of the fungi 

 commonly termed mushrooms or toadstools.^ 



1 A good systematic account of the class as it appears in Great Britain, a work which ia 

 the absence of one specially adapted to this country is exceedingly helpful to a student, is 

 Stevenson's " llymenomycetcs Britannici." 



