220 



PTERIDOPHYTA. 



germination, water is absorbed, the two sides separate slightly, aa 

 valves (Fig. 220 A), and a long vermiform mass of gelatinous, 

 parenchymatous cells (Fig. 220), swollen by the water, emerges, 

 bearing a large number of sori arranged pinnately. Each sorus 

 (sr) is covered by a thin indusium. (The thin covering may be 

 considered an indusium physiologically, though not morpho- 

 logically). 



Marsilia quadrifolia, in Europe. Many species are found in Australia. The 



FIG. 220. Marsilia salvatrix : A the 

 eporocarp commencing to germinate; B 

 a more advanced stage of germination. 



FIG. 221. Pilularia globulifera (natural 

 size) : s sporocarps ; b leaves ; fc the 

 growing point; r roots. 



nutritious sporocarps of M. salvatrix were the means of saving the Burke ex- 

 pedition in the interior of Australia, and hence this species lias earned its specific 



Pilularia has linear leaves, without lamina. The sporocarps are 

 spheroid (Fig. 221), brown and hard, and situated near the base of 

 the leaves. They are 2-4 chambered and open by a corresponding 

 number of valves. 



