THALLOPHYTA. 689 



is Dcedalia (fig. 390 2 ) a bracket-like form in which the hymenium takes the form 

 of irregular branching slits on the under surface. The Agaricinece, which include 

 the very numerous mushroom and toadstool Fungi, are for the most part umbrella- 

 like in form, having a central stalk and expanded circular receptacle (the pileus). 

 The under surface of the pileus is occupied by lamellae or gills which radiate from 

 the insertion of the stalk to the margin of the pileus (cf. figs. 390 3 ' 4 > 6 ). The 

 basidia forming the hymenium are set upon the sides of these gills. Fig. 389 x 

 shows an enlarged section through a part of a gill. In the more complex forms 

 certain structures are present inclosing the young fructification, but they are 

 ruptured as the pileus expands, and in adult fructifications the gills are freely 

 exposed. Their remains may often be seen on the mature Fungus, as in Amanita 

 (fig. 390 6 ). Just below the pileus there is a membranous ring (the annulus)', at 

 an earlier period it was attached to the margin of the pileus covering in the 

 hymenium, and forming what is termed the velum partiale. In the same Fungus 

 may be noted the remains of another sheath, the velum universale, which en- 

 wrapped the entire fructification. This is shown in fig. 390 6 as a ruptured sheath 

 (the volva) at the base of the stalk, whilst portions of the covering which invested 

 the pileus (and was continuous with the ruptured sheath alluded to) are to be seen 

 as white felty patches on the top of the scarlet pileus of Agaricus muscarius. 

 The forms and varieties of the Agaricineae are far too numerous even for mention. 

 Many of them are edible, notably the Mushroom, Agaricus campestris, Pholiota 

 mutabilis, and the yellow-coloured Cantharellus cibarius (allied to the Agaricineae). 

 Others again are poisonous, as, for instance, the scarlet Agaricus muscarius just 

 cited, which receives the name muscarius from the fact that decoctions of 

 this Fungus were formerly used for killing flies. Certain forms (Russula and 

 Lactarius) contain a latex of a white or yellow colour. A number are character- 

 ized by producing sclerotium-like bodies (cf. p. 681). As a rule in the Agarics the 

 fructifications arise directly from the mycelium, but in Coprinus stercorarius, 

 Lentinus, &c., tuber-like masses of fungal substance are formed, and it is from 

 these that the fructifications arise. These sclerotia, often attaining large dimen- 

 sions, have been found by travellers in various parts of the world, and the fructifi- 

 cation which arises from them is not in all cases known. Several of them, formerly 

 name Pachyma, &c., are now known as belonging to the genus Lentinus. Very 

 curious are the string-like sclerotia of Agaricus melleus which, from their root- 

 like nature, were formerly termed "Rhizomorphs". They are found especially in- 

 Conifers, growing between the wood and bark, and having a ribbon-like form; from 

 them cylindrical branches may arise which penetrate the soil and attack the root of 

 some other tree. Ultimately the mushroom-like fructifications arise from thes& 

 rhizomorphs. 



A few lichens derived from the Hymenomycetes are treated at p. 695. 



Gasteromycetes. These are characterized by the fact that the basidia arise ii* 

 closed chambers, which collectively constitute the gleba, and that this is covered by 

 a continuous cortex or peridium. They include the Puff-balls, Earth-stars, Stink- 



VOL. II. 94 



