CHAPTER Tin 



THE GEBAT GROUPS OF BRTOPHYTES 



HEPATiCiE {Liverii'orts) 



68. General character. — Liverworts live in a variety of 

 conditions, some floating on the water, many in damp 

 places, and many on the bark of trees. In general they are 

 moisture-loving plants (hydrophytes), though some can en- 

 dure great dryness. The gametophyte body is jji'ostrate, 

 though there may be erect and leafless gametophores. 



This prostrate habit develops a dorsiventral body — that 

 is, one whose two surfaces {dorsal and ventral) are ex2)(jsed 

 to diilerent conditions and become unlike in structure. In 

 Liverworts the ventral surface is against the substratum, 

 and puts out numerous hair-like processes (rhizoids) for ab- 

 sorption and anchorage. The dorsal region is exposed to 

 the light and its cells develop chlorophyll. If the thallus 

 is thin, chlorophyll is developed in all the cells ; if it be so 

 thick that the light is cut off from the ventral cells, the 

 thallus is differentiated into a green dorsal region doing the 

 chlorophyll work, and a colorless ventral region producing 

 absorbing rhizoids. This latter represents a simple differ- 

 entiation of the nutritive body into working regions, the 

 ventral region absorbing material and conducting it to the 

 green dorsal cells which use it in making food. 



There seems to have been at least three main lines of 

 development among Liverworts, each beginning in forms 

 with a very simple thallus, and developing in different di- 

 rections. They are briefly indicated as follows : 



109 



