REPRODUCTION OF THE FERN 



127 



Development. The fertilized egg cell or oospore begins at once 

 to divide, first into two, then into four cells. Of these first four 

 cells, two form the foot or attachment organ by which the young 

 embryo retains its position in the tissues of the prothallium ; 

 em. 



rh. 



FIG. 51. Development of the fern embryo. A, Section showing the closed 

 neck () and the planes of division of the embryo into four cells (em) ; B and C, 

 later stages of the embryo showing the beginning of apical growth and formation 

 of the first leaf and rhizome. The other figures represent later stages in develop- 

 ment, ar, old archegonia; /, foot; I, leaf; p, prothallium; r, root; rh, rhizoids. 

 (From Sedgwick and Wilson, after Hofmeister and Sachs.) 



one forms the rhizome, and one the first frond or leaf (Fig. 51). 

 The young fern thus develops while anchored to the sexual 

 generation. A second leaf is soon started from the basal por- 

 tion; the first leaf unfolds in the light and the cells become filled 



