LIFE HISTORY OF A FERN 



165 



very 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 beU-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. 



151. 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 



