536 



BOTANY OF THE LIVING PLANT 



catches them and is then absorbed. Thus the pollen- grains are landed 

 directly on the apex of the nucellus, where they are constantly to be 

 found in sections cut through the ovule {p, Fig. 423). Excepting 

 that there is no receptive stigma the process is not unlike that in 

 wind-pollinated Angiosperms. 



Differences of great comparative interest lie in the details 

 within the ovule itself. The ovule originates as in Angiosperms, 

 and as in them the embryo-sac is one cell of a tetrad produced 



- 0/ 



Fig. 424. 

 Picea vulgaris. A = longitudinal section through apex of female prothallus, and 

 one archegonium. n=neck. v.cc = ventral canal cell. <w = ovum. B = neck seen 

 from above. C = entry of pollen-tube with gametes into the canal of the arche- 

 gonium. (A x 100 ; B, C x 250.) (After Strasburger.) 



in the young nucellus ; its nucleus is therefore haploid. (See 

 p. 297.) But an essential difference is that in Pinus, and all other 

 Gymnosperms, nuclear division proceeds to a high number in 

 the young embryo-sac. Cell formation follows, and the sac is thus 

 filled before fertilisation by a bulky tissue of the endosperm, or 

 female prothallus (Fig. 423, e). At the time of fertilisation, which 

 in Pinus and Picea happens about the middle of June of the 

 year after pollination, the female prothallus bears at its micro- 

 pylar end three to six large archegonia, of which two commonly 

 appear in a median longitudinal section of it (Fig. 423, a). Each of 

 these originates from a single superficial cell of the prothallus, and 



