EUMYCETES 



29 



Class III. Basidiomycetes. 



These include by far the greater number of those plants which are 

 popularly known as " fungi," i.e. all the mushrooms, toadstools, puff-balls, 

 stinkhorns, "bird's nest fungi," and "bracket fungi" (on tree-trunks), etc. 

 The class is characterised by the formation of a special type of spore, called 

 the bdsidiospOYe. These are produced in definite numbers (generally four, 

 rarely two or three) on the outside of a stout hypha called the basidiwwi. 

 The basidia, except in one or two of the very simplest forms, are grouped 

 closely together in a hymeyiiwvn^ and the families are based to a large 

 extent on the position and extent of the hymenium. 



The two main sub-divisions* are the Hymenomycetes, in which 

 the hymenium is freely exposed before the spores are mature, and the 

 Gasteromycetes, in which the hymenium is completely enclosed until 

 (or after) the spores are ripe. Of the Hymenomycetes 

 the best known and largest family is the Agaricaceae, 

 to which the ordinary edible mushroom belongs as well 

 as some very poisonous species. 



Agaricaceae. Examples of this family are shown 

 in Plate 4, Fig. B (the edible mushroom), Plate 3, 

 Fig. C (the "death cup"), and Plate 4, Fig. C (the fly- 

 mushroom). The two latter are exceedingly poisonous, 

 nearly all the cases of mushroom-poisoning being caused 

 by the " death cup." 



The main points in the structure and development 

 of the common mushroom, Psalliota campestris, are : 

 The vegetative part, the spawfl y consists of rather 

 thick strands of hyphae which spread in the soil. On 

 these the mushrooms first appear as little swellings. The 

 mature spOTOphove consists of a stalk and an umbrella- 

 shaped cap, called the piletts Half-way up the stalk 

 are the remains of a thin white membrane, forming a 

 ring round the stalk, called the anntiltts. On the 

 lower side of the pileus are a number of radiating 

 lamellae or gills. On the outer surface of the gills 

 (forming the hymenium) are the basidia, each of which 

 bears from two to four small basidiospores. Mixed with 

 these are the pCLYCLphyses, which resemble the basidia 

 but are sterile. Figure 23 shows a small part of the 

 hymenium in a related plant. These mushrooms are rarely reproduced by 



Fig. 22. Pezi-za spec 

 Ascus and paraphy- 

 ses, 300/1. w.t.s 



* Some of the smaller groups, e.g. the smut diseases and the quivering fungi, have 

 been omitted in order to simplify the classification here given. 



