FLOWERLESS PLANTS. 179 



these little brown patches answer, in a certain way, to 

 seeds. It is from them that new ferns arise. They are 

 the reproductive parts of this class of plants, and the 

 fronds that bear them are said to be fertile. Examine 

 these spots carefully with your magnifying-glass, and com- 

 pare them with Fig. 468 or Fig. 472. The small, brown- 

 ish clusters of fruit-dots seen on the under surface of 

 fronds, in rows along the veins, or on the margin of the 

 pinnae, are called sort, and a single cluster a sorus. The 

 scale or protective covering of a sorus, seen in Fig. 472, 

 but absent in Fig. 468, is called an indusium. This organ 

 is still more plainly seen in Fig. 473. 



In the sorus (Fig. 473) you see little, peculiar-looking 

 bodies escaping from beneath the indusium. Each of 



FIG. 475. 



these cell-like bodies, of which the sorus is composed, is 

 known as a spore-case, sporange, or theca. They are some- 

 times stalked, as seen in Fig. 474. The singular-looking 

 band around them is an elastic membrane, which bursts 

 when they are mature, and thus the spores contained in 

 the spore-case escape (Fig. 474, A). It is from spores that 

 ferns arise, but by a process more like budding than like 

 the sprouting of a seed. When a spore commences to 

 grow, appearances like those represented in Fig. 475 may 

 be observed. The growth begun by a spore, as at a, and 

 seen more advanced at b, is shown at c, expanded into a 

 leaf-like body, called a prothallus, which gives off roots at 



