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 



' 'v >r---y 



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 



