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 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. 
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 
