FUNGI. 551 



adhering to stones, rocks, trees, &c. During part of their growth, 

 they appear to be capable of deriving most of their nourishment from 

 the atmosphere. They have the power of acting on hard rocks, so 

 as to disintegrate them in process of time, and many of them contain 

 much inorganic matter in then- composition. They all grow in the 

 air ; none are found submersed. 



1120. The order has been divided into four sections: 



1. Hymenothalamese (i,-<>, a membrane, 8ax*,u<x, a receptacle): shields open, 



discoid permanent nucleus bearing the sporangia on its surface (fig. 780). 



2. Gasterothalamece (rao-r^, a belly) : shields either closed always, or opening 



by bursting through the cortical layer of the thallus, the nucleus containing 

 the deliquescing or shrivelled sporangia. 



3. Idiothalameaj (<&;, peculiar) : shields closed at first, opening afterwards, 



containing free spores in a nucleus composed of the gelatinous remains of 

 the paraphyses and sporangia. 



4. Coniothalameae (*n?, powder), pulverulent lichens : shields open, without a 



nucleus, cavity filled with free spores. 



1121. Lichens furnish articles of food and important dyes. Cetraria 

 islandica, commonly called Iceland Moss, contains a nutritious matter 

 called Lichenin, or Lichen- starch. There exists in it a bitter principle 

 also, to which the name Cetrarin has been given. The plant is used 

 as a demulcent and tonic, in the form of decoction or jelly. Cla- 

 donia rangiferina is a Lichen upon which the Reindeer feeds. Several 

 species of Gyrophora constitute the Tripe de Roche, on which Franklin 

 and his companions subsisted for some time. Many other Lichens, 

 such as Sticta pulmonaria, and species of Lecanora, furnish articles of 

 food. Roccella tinctoria from the Canaries, and E. fuciformis, furnish 

 valuable dyes, under the name of Orchil or Archil. The dye procured 

 from them, and from other Lichens, is called Litmus. Lecanora tar- 

 tarea supplies the dye called Cudbear. Parmelia parietina contains a 

 yellow colouring matter called Parietin or Chrysophanic acid. Some 

 species of Variolaria contain a large quantity of oxalate of lime. 

 Some plants of the order are aromatic. 



1122. Order 219. Fungi, the Mushroom Family. The plants be- 

 longing to this order consist of cells, sometimes round, sometimes 

 elongated in the form of filaments, either placed closely together or 

 separated. They are variable in their consistence, being soft or hard, 

 fibrous or gelatinous, fleshy or leathery. They never contain green 

 gonidia like Lichens, and they rarely grow in water. There exists a 

 vegetative system called spawn or mycelium (^VX.YI;, fungus), formed 

 of elongated, simple, or articulated filaments, concealed within the 

 matrix, or expanded over its surface, from which varied forms of fruc- 

 tification proceed. The mycelium occurs either in a filamentous, a 

 membranous, a tubercular, or a pulpy form. The reproductive organs 

 consist of spores or spherical cells (usually 4 or some multiple of 4), 

 which are either attached to the cellular tissue, and supported often 



