II 



MUSCINEyE—HEPA TIC^—MARCHANTIA CE.-E 



which condition they remain dormant until the autumn rains 

 begin, when they absorb water and begin to grow again at once. 

 In these cases usually only the ends of the branches remain 

 alive, so that each growing tip becomes the beginning of a new 



plant. 



T/ie RicciacecB 



As a type of the simplest of the Marchantiaceae, we may 

 take the genus Ricda, represented, according to Schiffner,^ by 

 107 species, distributed over the whole earth. Most of them 

 are small terrestrial plants forming rosettes upon clay soil, or 

 sometimes on drier and more exposed places. A few species, 

 e.g. R. fliiitans, are in their sterile condition submersed aquatics, 

 but only fruit when by the evaporation of the water they come 

 in contact with the mud at the bottom. 



Fig. -x.—Riccia glauca (L.). Development of the archegonium, X525. A, Vertical section throut^h 

 the growing point ; .r, apical cell ; ar, young archegonium ; //, ventral lamellae ; B-F, successive 

 stages in the development of the archegonium, seen in longitudinal section ; G, cross-section of 

 young archegonium (diagrammatic). 



The dichotomously branched thallus shows a thickened 

 midrib, which is traversed upon the dorsal surface by a longi- 

 tudinal furrow which in front becomes very deep. At the 

 bottom of this furrow, at the apex of the thallus, lies the growing 

 point. A vertical section through this shows a nearly triangular 



^ Schiftner (i), p. 14, 



