552 



LIFE-HISTORIES 



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Fig. 379. — Norway Spruce. Fertilization of egg-cell. A. ripe egg-cell with 

 nucleus (on) and lower neck-cell (cl), -c- B, same, later, the tip of a 

 pollen-tube (p) having entered the egg-cell and discharged into it the 

 male nucleus (sw) which approaches the female nucleus (o«)- C, same, 

 later, the two nuclei having become fused into one, which soon divides 

 into four nuclei that move to the lower end of the egg-cell. D, lower 

 end of the egg-cell showing two of the four nuclei which have moved 

 into it. E, same after division of the four nuclei into eight. F, same 

 after further division has produced four tiers of nuclei, all but the 

 uppermost four being enclosed in cell-walls. G, same, after the middle 

 tier of cells has elongated to form a suspensor which has pushed the 

 lower tiers of cell into the prothallus (or endosperm) where they give 

 ri.se, by repeated cell-division, to an embryo which is fed by the endo- 

 sperm. The nutritious materials left over in the endosperm when the 

 oxTile has become a seed constitutes the seed-food which supports the 

 young plantlet during germination. (Strasburger.) 



spreading carpel, they come finally to the micropyle where the 

 integument is often prolonged in such a way as to lead them directh'^ 

 to the tip of the nucellus. Here they germinate Iw forming a few 

 cells, some of which, remaining within the spore, represent the vege- 

 tative part of the male gametoph}i:e; while others, the male gametes, 

 form a hypha-like tulie which penetrates the soft tissue of the 

 nucellus and feeds upon it like a fungus. Meanwhile the macrospore 



