SPERMATOPIIYTES : GYMNOSPEKMS 



179 



ne L z_ 



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 8e- 

 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. So conspicuous a tissue 

 within the ovule, as well as in the seed into which the 



Fig. 149. Diagrammatic section through ovule 

 (megasporangiiim) of spruce {Picea), showing 

 integument (i), nucelhis inc), endosperm or 

 female gametophyte (e) which fills the large 

 megaspore imbedded in the nucelhis, two 

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

 containing the egg io). and position of ger- 

 minating pollen grains or microspores (p) 

 whose tubes (0 penetrate the nucelhis tissue 

 and reach the archegonia. — After Schimper. 



