CRYPTOGAMS AND PHENOGAMS 551 



nc — I 



Fig. 378.— Norway Spruce. Ovule cut vertically and enlarged to show the 

 embryo-sac (c) filled by the prothalhis or endospertn and two archegonia 

 (a), each with its neck (c) and swollen part (o) which contains an egg- 

 cell with a nucleus {n); the nuctllus (nc) surrounded by the integuments 

 (i) ; pollen-grains (p) from which come pollen-tubes (0 extending to the 

 archegonia; and a part of the seed-wing (s). (Strasburger.) 



Pinus and related genera will doubtless be sufficiently clear without 

 further explanation, but the carpels and ovules call for more de- 

 tailed examination. Each carpel, as we have seen, bears two ovules 

 on its upper side near the base (Fig. 258, 8). When cut in half 

 vertically such an ovule exhibits the parts shown in Fig. 378. A 

 single macrospore organically connected with the surrounding tissue 

 constitutes what is termed the embryo-sac (e) . The rest of the ovule 

 represents the macrosporangium, which is divided into a central 

 part, the 7iucellus ^ (nc) in which the embryo-sac is embedded, and 

 an outer layer, called the integument (0, which covers the nucellus 

 except at the micropyle. Microspores, i. e., pollen grains, intrusted 

 to the wind, are carried to the pistillate flowers. Caught by a 



1 Nu-cel'lus < L. nucella, a little nut. 



