THE PAGE OF NATURE. 51 



treated with different chemical tests, from their trans- 

 parency and variety of colouring. One ally of this genus, 

 called Biella, differs widely from the rest of the tribe in 

 its erect, moss-like habit. It grows on the margins of 

 ponds, streams, and lakes in Algiers and Sardinia, and 

 perfects its fruit when submerged. It is quite a botani- 

 cal curiosity, presenting a whorled appearance, not unlike 

 the common spiral shells of the sea-shore. Each indi- 

 vidual consists of a central stem, round which a distinct 

 leaf or wing is wound in the form of a screw or continu- 

 ous spiral. On the edge of this wing, towards the sum- 

 mit of the male plant, the antheridia are developed ; 

 while in the female the fruit clusters on the stem between 

 the whorls. 



The most interesting of all the scale-mosses is the com- 

 mon marchantia or liverwort (Marcliantia polymorpha, 

 Fig. 3). It is very common, creeping in large, dull, 



FIG. 3. MARCHANTIA POLYMORPHA. 



dark- green patches over rocks in very moist and shady 

 situations, such as the banks of a densely-wooded stream 

 in a deep narrow glen, or the sides of rivers and foun- 

 tains. It may often be seen also on the moist walls of 



