124 



PLANTS, THE FOOD OF ANIMALS 



The entire process of fertilization takes place within the tissues 

 of the prothallium. 



Development. The fertilized egg cell or oospore begins at once 

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



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. (From Sedgwick and Wilson, after Hofmeister and 

 Sachs.) 



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

 embryo retains its position in the tissues of the prothallium, 

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

 The young fern thus develops while anchored to the sexual 



