SECT. VI. 



MAR CHANT I A CE&. 



317 



taining spermatozoids ; in the female plant the spo- 

 rangia spring from the stem ; they have a separate en- 

 velope, and the spores are echinate. 



The Marchantiacese rank as higher forms of Hepaticse. 

 In the Marchantia polymorpha (figs. 43, 44), which may 

 be taken as an illustration of the group, the structure 

 of the horizontal frond is complicated, for, besides the 

 colourless transparent skin, there are three distinct 

 layers, the uppermost of which consists of cells filled 

 with green matter, the lowermost (or base of the frond) 

 being formed of close-set cells full of very solid matter, 

 while between the two there is a cavity filled with air 

 and loosely branching fila- 

 ments, which spring from 

 the base, and consist of 

 green cells fixed end to 

 end, as in fig. 44 B. The 

 surface of the plant ap- 

 pears to be smooth and 

 shining, but when mag- 

 nified it is found to be 

 marked with numerous 

 narrow elevated green 

 bands, crossing one an- 

 other diagonally so as to mark out the surface into a 

 number of small lozenge-shaped divisions (fig. 44 A). 

 These elevated bands are merely the tops of very solid 

 walls which descend perpendicularly to the base of the 

 plant, consequently they divide the internal air chamber 

 into a number of lozenge- shaped compartments, each of 

 which communicates with the external atmosphere by 

 means of chimneys opening in the centre of each com- 

 partment on the surface of the plant. These chimneys 

 are so constructed of four or five superposed rings of 

 cells (see fig. 44 B), that by the expansion and contrac- 

 tion of the cells of the lowermost ring, more or less air 



Fig. 43. Marchantia polymorpha : a, gem- 

 miparotis conceptacles ; b, lobed receptacles 

 bearing pistillidia. 



