FERNS 



The spores are so minute and light that, in a 

 dry atmosphere, they get wafted for considerable 

 distances. By this means, too, they land in all 

 sorts of curious situations ; thus we frequently find 

 ferns growing from the mortar between the bricks 

 of a wall (Fig. 121, Plate 85) ; or from the bark of 

 the shaded branches of trees that overhang rivers 

 and moist places, and in other similar positions. 

 The most remarkable fact, however, is that these 

 spores, when they develop, do not produce ferns ; 

 indeed, the structures that originate from them are 

 something altogether different. 



When the tiny spore reaches a damp and warm 

 place with plenty of light, it sends out a tubular 

 development which extends its tissues by division 

 of its cellular structure ; first it increases in length, 

 and later transversely. Ultimately, by the con- 

 tinual division of the cells of which it is composed, 

 a flat plate of green tissue is produced. This little 

 heart-shaped structure, known as the prothallus, 

 ' develops on its under surface delicate " root-hairs," 

 which attach it to the soil. A magnified view ot 

 the whole structure is shown in Fig. 120 (Plate 86). 



Thus we see the fern spore produces not a fern, 

 but a little plant-like structure consisting of a 

 heart-shaped green scale which rests upon the 

 surface of the soil, and which in actual size is 

 scarcely one-fifth of an inch in diameter ; yet its 

 green tissues can absorb gaseous food from the 

 atmosphere, and its tiny root-structures can supply 

 all its needs from the soil. 



This cuiious little structure exists perhaps for 



195 



