318 



THE PTERIDOPHYTES 



sperms swim down the neck to the egg, and one of them fer- 

 tilizes it. The fern plant then, like the liverwort and moss, 

 practically returns to the aquatic life of the algie at the time 

 when the sexual cells are functional. 



309. The development of the sporophyte. The early stages in 

 the development of the fern sporophyte as in the hryophytes 



FIG. 279. Development of the sporo- 

 phyte of a fern 



A, section of prothallinm with a young sporo- 

 phyte : c, thickened region, or cushion, in which 

 is imhedded the foot; I, first leaf: r, root; ar, 

 unfertilized archegonia : <///, old antheridia; 

 rh, rhizoids. B, an old prothallinm with young 

 fern sporophyte attached, whose first leaf I has 

 grown up through the notch at the forward end 

 of the prothallinm, while the root r has entered 

 the earth: rh, rhizoids. After Sachs 



rh 



are passed entirely within the tissue 

 of the prothallium, surrounded by the 

 remains of the archegonium. The ferti- 

 lized egg cell divides, and there are 

 formed four regions in the embryo 



fern : (1) a stem region, (2) the first leaf, (3) the first root, and 

 (4) an organ of attachment to the gametophyte called the foot. 

 The leaf and root soon break out of the archegonium, the first 

 growing upward and the second into the earth (Fig. 279, A, B). 

 The stem grows more slowly. The young fern all this time 

 obtains nourishment from the prothallium through the foot after 

 exactly the same method as in the bryophytes. However, when 



