LIFE HISTORY OF A FERN 165 



vefy small percentage of them would be able to develop 

 into new plants. When the spores are ripe, the spore-case 

 opens, and by various movements the spores are expelled. 

 That sporangia are able to throw the spores to a 

 considerable distance may be shown in a very simple 

 way by placing a portion of a sporophyll with mature 

 sporangia on a sheet of white paper, with the fruit-dots 

 uppermost, and covering it with a large bell- jar. Within 

 a few hours the scattered spores may be seen against 

 the white background of the paper, and the greatest dis- 

 tance to which they have been thrown may be easily 

 measured (Fig. 124). 



FIG. 125. Germination of the spores of a fern, a, Before germination; 

 b, early stage, showing protonema (pr.\ and first rhizoid (rh); c, d, e, f, 

 successive stages in the development of the prothallus. 



161. Germination of Spores. After dispersal, and 

 under favoring conditions of temperature, moisture and 

 light, the spore begins to absorb water, and soon com- 

 mences to grow. As the internal osmotic pressure in- 

 creases, the walls of the spore are burst apart, and a tiny 



