PRINCIPAL GROUPS OF PLANTS. 109 



gametophyte (Fig. 70, E; Fig. 71). In the upper portion of the 

 prothallus (that is, at the micropylar end), three to five archegonia 

 are formed (Fig. 70, a; Fig. 71), which are separated from one 

 another by cells of the endosperm or prothallus, which are rich in 

 protoplasm. The structure of the archegonium is much like that 



nc 



FIG. 70. Longitudinal section of an ovule of a spruce (Picea): i, integument; nc, 

 nucellus (megasporangium) ; e, embryo-sac (megaspore) which has developed the female 

 gametophyte consisting of endosperm (e), two archegonia (a), which show the neck (c), 

 and the egg (n); p, germinating pollen grains (microspores) with pollen tubes (t) which 

 have penetrated the nucellus (nc) and reached the neck cells of the archegonia. After 

 Schimper. 



of the preceding group, consisting of a venter which contains the 

 egg, and a short neck composed of 4 to 8 cells. 



The male gametophyte begins to develop while the pollen is 

 still in the sporangium. At this stage it consists of a generative 

 cell and a wall-cell, which constitute the antheridium, the cells of 

 the prothallus being usually suppressed (Fig. 69, D). 



In addition to the extreme minuteness of the gametophytes 



