SPEKMATOPIIVTES : G VMNi ISI'EUMS 



170 



ne 



pine the micropyle is directed downward, toward the hase 

 of the sporophyll (Figs. 147, 118). 



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 .S'c- 

 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. 119, 

 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 wdthin its tis- 

 sues like an internal parasite, 

 within the ovule, as well as in 



Fig. 149. Diagrammatic section throu2:h ovule 

 (megasporangium) of spruce iPicea). showing 

 integument (H, nucellus (nc), endosperm or 

 female gametophyte (e) which fills the large 

 megaspore imbedded in the nucellus, two 

 archegouia (a) with short neck (c\ and. venter 

 containing the egg (o). and jio-^icioi^ of ger- ^ 

 minating pollen grains or microspores (p) 

 whose tuhes it) penetrate the nucellus tissue 

 and reach the archegouia.— After Si iip.rrER. 



So 

 the 



conspicuoi^s a tissue 

 seed into which the 



