CRYPTOGAMIA. 



fier in order to detect their different parts. They are found 

 on rocks, old walls, the bark of trees, and some of them in 

 damp, shady bogs. 



Fig. 214 



The small figure, 214, represents one of the 

 Jungermannia species of the natural size. The 

 larger, is the same magnified, showing the four- 

 valved thecae at the top, after it has burst and dis- 

 charged its seeds. This species is called Dwarf 

 Jungermannia, and grows in small patches on 

 rocks. Leaves elliptical-ovate ; fruit terminal ; 

 mouth contracted and toothed ; pedicel half an 

 inch high. 



This genus is named after Louis Jungermann, a German 

 botanist. 



ORDER VII. ALG^E. Flags. 



In this order the seeds are embedded in the substance of 

 the frond, or in the thecae, or tubercles variously situated 

 The plants are nearly all aquatic and submerged. 



The order consists of the sea-weeds of the ocean, and the 

 floating, scum-like substance of ditches and rivers. The 

 fronds are sometimes thick and cylindrical, and sometimes 

 they are like ribbons, extending many yards in length. 



In other instances, this kind of vegetation is nothing more 

 than a mere membrane, or a tuft of fine threads. The Sea 

 Flags are in general fixed to rocks or stones by small expan- 

 sions, or sometimes to the sand or mud by roots. It is sup- 

 posed that their nourishment is imbibed from the water by 

 their surfaces. 



Figure 215 represents one of the most com- 

 mon species of this genus, the Knotty Fucus, 

 (Fucus nodosus.} It grows on stones and rocks 

 near the shore of the sea. Frond compressed 

 and leathery ; here and there inflated with inter- 

 nal vesicles. These contain air, and therefore 

 when heated or compressed, they burst with a 

 small explosion. This and the other species of 

 Fucus are burned for their ashes, which, when 

 purified, form the soda of commerce. The im- 

 pure product of the burning is called kelp. 



The Flags form one of the lowest orders of vegetation, 



To what important use are the sea-weeds converted ? 



Fig. 215. 



