94 A LEAFY LIVERWORT. 



for oospores just beginning to develop the sporophyte, 

 and also old sporophytes which contain ripe spores. 

 Draw. 



ANNOTATIONS. 



The plant body of the leafy liverworts differs from 

 that of the forms already studied in that it has specialized 

 stem and leaves, better adapting it for chlorophyll 

 work. The leaves are arranged in three rows and 

 are simply lateral outgrowths from the stem. The 

 rhizoids are comparatively few in number and arise 

 from the ventral side of the stem at its base. Al- 

 though the plant has basal and apical regions and the 

 leaves are arranged around the stem, it is essentially 

 dorsiventral because of the unlikeness of the leaves 

 above and below, and of the occurrence of rhizoids 

 chiefly on the ventral side. The plant is prostrate, 

 though the tip sometimes becomes erect. In some 

 ways the plant is far better organized for nutritive work 

 than any that have yet been considered. 



In Porella the branches that bear the reproductive 

 organs are not set apart entirely for reproductive work, as 

 was the case in Marchantia. In general structure the 

 archegonium is essentially similar to that of Marchantia, 

 while the antheridium is not sunk beneath the surface as in 

 the other liverworts studied, but is free and has a support- 

 ing stalk. Fertilization takes place and the oospore devel- 

 ops into the sporophyte as in Marchantia. The sporo- 

 phyte has distinct foot, stalk, and capsule regions. When 

 it has ripened its globular mass of spores they are set 

 free by having the capsule split into four valves, and 

 eventually develop new leafy plants. 



