8PEBMATOPHYTES : GYMNO8PERMS 



179 



nc 



pine the micropyle is directed downward, toward the base 

 of the sporophyll (Figs. 147, 148). 



99. Female gametophyte. The female gametophyte is 

 always produced by the germination of a megaspore, and 

 therefore it should be 

 produced by the so- 

 called embryo-sac with- 

 in the ovule. This im- 

 bedded megaspore ger- 

 minates, just as does 

 the megaspore of Se- 

 laginella or Isoetes, by 

 cell division becoming 

 filled with a compact 

 mass of nutritive tissue 

 representing the ordi- 

 nary cells of the female 

 prothallium (Fig. 149, 

 e). This prothallium 

 naturally does not 

 protrude beyond the 

 boundary of the mega- 

 spore wall, being com- 

 pletely surrounded by 

 the tissues of the 

 sporangium. It must 

 be evident that this 

 gametophyte is abso- 

 lutely dependent upon 

 the sporophyte for its 

 nutrition, and remains 

 not merely attached to 

 it, but is actually im- 

 bedded within its tis- 

 sues like an internal parasite, 

 within the ovule, as well as in 



FIG. 149. Diagrammatic section through ovule 

 (megasporangium) of sprnce (Picea), showing 

 integument (i), nucellns (nc), endosperm or 

 female gametophyte (e) which fills the large 

 megaspore imbedded in the nucellus, two 

 archegonia (a) with short neck (c) and venter 

 containing the egg (0). and position of ger- 

 minating pollen grains or microspores (p) 

 whose tubes (t) penetrate the nucellns tissue 

 and reach the archegonia. After SCHIMPER. 



So conspicuous a tissue 

 the seed into which the 



