LICHEKES. 



549 



closed in involucres and solitary (fig. 778 i e), or occurring at the 

 edge of the frond, or on the lower 

 side of stalked peltate expansions 

 (fig. 412). Thecse or developed 

 pistillidia, having no operculum, 

 opening irregularly, or by four 

 valves (fig. 778). Spores (fig. 498) 

 often mixed with spiral filaments 

 called Elaters (fig. 779). Hetero- 

 rbizal in germination (fig. 530). 

 Terrestrial plants found in damp 

 places, or inhabiting water; some 

 having a moss-like appearance. They 

 are natives both of cold and warm 

 climates, and are generally distri- 

 buted over the globe. 



1117. The order has been divided into three sections: 1. Mar- 

 chantiea? : theca3 collected in heads, bursting irregularly, no opercu- 

 lum, spores with elaters. 2. Jungermanniete: thecse solitary, opening 

 by four valves, no operculum, spores with elaters. 3. Eicciese: thecae 

 solitary, decaying so as to allow the spores to escape, no operculum, no 

 elaters (fig. 411). Many of the Hepaticas produce gemmae or buds, 

 which are developed on the frond in the form of cup-shaped receptacles, 

 and ultimately fall off so as to become distinct plants. Marchantia 

 hemispherica has been recommended in dropsical cases. There are, 

 according to Lindley, 65 genera, and about 700 species. Examples 

 Marchantia, Jungermannia, Riccia. 



Subclass 2. THALLOGEN.E* OR CELLULARES. 



1118. Acotyledons composed entirely of cellular tissue, having no 

 distinct axis, nor leaves, nor stomata, propagated by means of spores, 

 which are often enclosed in asci. It corresponds to Endlicher's divi- 

 sion of Thallophyta, and includes the Amphigamse of De Candolle. 



1119. Order 218. Uchencs, the Lichen Family. Plants forming 

 a thallus, which is either foliaceous, crustaceous (fig. 780), or pulveru- 

 lent; these different forms depending on the mode hi which the cells 

 are developed and combined. The reproductive organs appear on the 

 frond in the form of protuberances of various kinds, consisting of an 

 outer layer of thick-walled roundish cells, more dense than the tissue 



* &x>.\ti;, a green leaf; yittiu, I produce. 



Figs. 778, 779. Organs of fructification of Jungermannia Tamarisci, to illustrate the natural 

 order Hepaticse. 



Fig. 778. -f, Branches covered with imbricated leaves, arranged in a distichous manner. Two 

 of the branches bearing thecas, supported on stalks which arise from an involucre at the base. 

 i ?', Involucres, c, Theca closed in the young state. <?, Theca opening by four valves to discharge 

 the spores and elaters. 



Fig. 779. r, Receptacle bearing elaters, e, or spiral filaments, one of which shows the double 

 spiral fibre. s, Free spores. 



