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APPENDIX A 



their higher degree of structural organization, related to the requirements 

 of life upon land, as we have already seen. 



The Liverworts (Hepaticae) are mostly found in moist situations, such as the 

 soil of seepage slopes, and rocks and tree trunks wet with spray or mist. A few 

 are aquatic, floating on the surface of ponds (Fig. 13.13). About 9,000 species have 

 been described; most of these are creeping thallus types, but some are upright 



Fig. A. 10. A thallus liverwort, Marchantia. A, gametophyte plant with antheridial heads. 

 B, swimming sperm. C, section of antheridium. D, section of antheridial head with antheridia 

 in place. E, gametophyte plant with archegonial heads. F, section of archegonial head with 

 archegonia in place. G, archegonium containing mature egg. an, antheridium; anh, antheri- 

 dial head; ar, archegonium; arh, archegonial head; ech, egg chamber; n, neck of arche- 

 gonium; ov, ovum or egg; spc, sperm-forming cells. (Modified from Turtox chart, courtesy 

 General Biological Supply House, Inc ) 



"leafy" forms. Marchantia is a common thallus liverwort often studied in the 

 classroom. It has a flat, ribbonlike form; the under surface is furnished with 

 simple rootlike filaments called rhizoids which serve for anchorage and absorption, 

 while the upper surface is covered with a cuticle and has numerous stomata. The 

 thallus is produced by cell division at an apical growing point (in a notch at the 

 tip) ; from time to time this growing point divides, so that the thallus bifurcates. 

 There is some differentiation among the cells but no vascular tissue. 



The life cycle of Marchantia (Fig. A. 10) is similar to that of the moss, described 



