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Practical Plant Biology. 



Its thallus for its body is not differentiated into stem, root, 

 and leaves is flat and ribbon-like, and grows over moist soil. It 

 is dark green in colour and shows many bifurcations. The ends 

 of the branches show deep indentations and their edges are 

 irregular and slightly crinkled. The indentations at the ends of 

 the branches mark the position of the growing regions of the 

 thallus. Passing back from these to the older parts a shallow 

 groove may be seen which marks the position of the mid-rib. 

 When the growing region divides to form a bifurcation naturally 

 the mid-rib divides too. If closely observed the surface of the 

 thallus on each side of the mid-rib may be seen to be marked out 

 into very small rhomboidal areas, and in the middle of each of 



FIG. 22. Marchantia polymorpha. A, plant with cupules, winter condition ; 

 B, plant with antheridiophores; C, plant with archegoniophores. 



these areas a minute red speck is seen. These areas mark the 

 position of air-chambers in the thallus immediately below the 

 superficial layer of cells, and the speck is a short tube or flue 

 perforating this layer and ventilating the chamber below. 



If the thallus is raised from the soil and its lower surface 

 studied, it will at first appear covered with the adherent soil par- 

 ticles. When they are removed the mid-rib is seen as a low ridge 

 running medianly in the thallus ; from the under surface spring 

 countless fine colourless hairs which penetrate among the particles 

 forming the surface of the soil and fix the plant to them. They 

 are called rhizoids. There are also numbers of irregular mem- 

 branous scales attached to this surface of the plant on either side 

 of the mid-rib, 



