29 



These strata were formerly supposed to be independent 

 Lichens, and constituted the genus Lepraria. Sometimes the 

 gonidia invade the apothecinm of Lichens, which gave rise to 

 another false genus, Variolaria. 3. A medullary, spongy, 

 filamentous, or cottony layer, composed of a network of 

 jointed delicate threads ; these are sometimes developed 

 downwards, forming rootlets or fibrils on the under surface 

 of many horizontal thalli. The hypothallus is a rudimentary 

 horizontal stratum, from which the thallus grows, and is 

 only clistiuguishable in the youngest state of the more 

 highly organised Lichens, and lies beneath the crustaceous 

 or granular thallus of the more lowly. 



The aj^othecia are usually discoid, dark-colored bodies, 

 occupying various portions of the thallus, rarely, however, 

 the under surface. In Nejjliroma they occupy the lower 

 recurved margin. They may be orbicular, linear (lirellate), 

 sessile or stalked, superficial or sunk in the thallus, convex, 

 concave, or sub-globose, and of all colors. The apothecia 

 consists oC the exciple or receptacle and thalamium. 



The receptacle is the enveloping portion of the apothecium, 

 and is formed of the substance of the thallus. When the 

 apothecium is adnate to the thallus, the receptacle only 

 borders it, and when the apothecium is peltate or stalked, 

 the receptacle forms its under surface also. When the 

 bordering portion is of the same color as the thallus, it is 

 ■called a thalline, or thallodal border ; when of a different 

 color, or that of the thalamium, it is called a proper border. 

 The receptacle may be altogether absent, or almost enclose 

 the thalamium, or form a globular capsule called a peri- 

 thecium. The thalamium is usually solitary in each recep- 

 tacle, but sometimes there are several, which are separate or 

 confluent. It consists of a series of vertical, elongate, 

 microscopic bodies, rising from a layer of minute cells, called 

 the hypothecium, and they are usually held together by a 

 transparent gelatine. The vertical bodies are two in number, 

 paraphyses and thecse or asci. The paraphyses are the most 

 numerous ; they are linear, subclavate, transparent jointed 

 bodies, whose terminal cells are thick walled, are often 

 -crustaceous, warted, colored, and adhering together from the 

 hard substance of the thalamium. The asci are shorter 

 vertical bodies, linear, clavate or ellipsoid, tapering down- 

 wards, and consist of simple, thick-walled transparent sacs 

 containing one or more, usually eight very minute spores. 

 At maturity the ascus breaks at the top, discharges the 

 spores and shrivels up, when fresh asci are developed from 

 the hypothecium, and this process goes on as long as the 

 apothecium, which is perennial, exists. The spores are 



