MARCHANTIA POLYMORPHA 365 



ii. The amphigastria, which may now be seen to 

 be plates of tissue one layer of cells in thickness : their 

 cell-walls are often coloured violet or brown. 



Returning now to the "stomata/' note under a 

 high power their structure as seen in a good transverse 

 section : each will appear as consisting of tiers of small 

 cells (four or more in depth), which surround a large 

 central cavity. 



IV. Cut tangential sections so as to strip off the 

 so-called " epidermis " : mount with the outer surface 

 uppermost in weak glycerine : observe under a low 

 power the diamond-shaped areas above described, and a 

 single large " stoma " in the middle of each. Under a 

 high power note 



1. That the cells of the " epidermis " contain 

 chlorophyll. 



2. That each " stoma " is bounded by four or five 

 of the tiers of cells above described. 



3. That these cells contain but little chlorophyll. 



4. That on focusing downwards it becomes apparent 

 that the lowest cell of each tier projects into the cavity 

 of the "stoma," so that the channel at that point 

 presents a stellate appearance in surface view. 



Sections should also be cut from the thallus of Lunularia, 

 wherein it will be found that the stomata do not correspond to 

 the above description, but are of a simpler type, and it is well 

 to compare the structure in Lunularia with that in Marchantia. 



Cut longitudinal sections of a mature thallus of Pellia 

 epiphylla : if the material be fresh, mount in water, if hardened 

 in alcohol mount in glycerine, and observe the almost uniform 

 structure of the tissues : the chlorophyll is chiefly located at the 

 upper surface ; the lowest layer of cells is coloured brown, and 



