MARCHANTIA POLYMORPHA 363 



of the sporogonium is raised upon the top of the greatly 

 elongated and transparent seta. 



Some species of Jungermannia should also be examined as an 

 example of the foliose Liverworts : here the shoot will be found 

 to be dorsiventral, but of more complex external form than that 

 of Marchantia ; in addition to the amphigastria, there are also 

 present lateral appendages or " leaves," which are thin, flattened 

 expansions of green chlorophyll-containing tissue, inserted on the 

 relatively thin axis. 



B. MICROSCOPIC OBSERVATION'S 



III. Cut transverse sections of the vegetative thallus 

 of Marchantia, avoiding at first the cups bearing the 

 gemmae, and the sexual branches. It is easier to use 

 material hardened in alcohol, and to embed it in 

 paraffin, or hold it between pieces of pith ; but if 

 sections be cut from fresh green material the presence 

 of chlorophyll will be found to be an advantage in 

 distinguishing the tissues. Mount some sections in 

 weak glycerine, others in chlor-zinc-iodine, or in 

 iodine solution : examine under a high power, and, 

 starting from the upper surface, observe 



a. The superficial layer, or so-called "epidermis," 

 consisting of a continuous layer of cells of small size 

 which contain chlorophyll, as may be seen in prepara- 

 tions from fresh material : the continuity of the layer 

 is broken here and there by the so-called " stomata " : 

 these, however, differ from the true stomata of the higher 

 plants in the mode of their development. This layer 

 may be seen to be attached to the lower-lying tissues at 

 points between the " stomata," and the lines of attach- 



