CONIFERALES 



343 



nuclear divisions the figures are entirely intranuclear, and there is a 

 great display of achromatic structures, especially at the first mitosis 

 (fig. 332). The next two mitoses follow in such rapid succession that 

 the entire free nuclear series may be secured at one collection (fig. 

 333). These four nuclei, which constitute all of the free nuclear pe- 

 riod, are formed at about the level of the egg nucleus. After the sec- 

 ond mitosis, they pass to the bottom of the egg, where the third mi- 

 tosis, closing with wall formation, takes place. 





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A 



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Fig. 331. — Sequoia sempervirens: first 

 division of the fertilized egg. A strong cell 

 plate is formed on the spindle, and the 

 wall will be completed before the second 

 division begins; X 500. — After Lawson.^'''' 



"'••^SmW- 



Fig. 332. — Piniis laricio: first division 

 of nucleus of fertilized egg. The figure is 

 entirely intranuclear; Xsoo. — After 

 Chamberlain."-' 



The positions of nuclei are worth noting. Throughout the develop- 

 ment of the archegonium, from the first appearance of the arche- 

 gonium initial up to the formation of the ventral canal cell, the nu- 

 cleus is at the top. After the ventral canal division, the nucleus 

 moves down to the middle of the egg; and after two mitoses, the four 

 nuclei move down to the bottom of the egg. Perhaps pollen tubes 

 and the disorganization of the nucellus may have something to do 

 with the earlier position, and nutrition, which, in later stages, comes 

 more from beneath, may cause the later movement. 



When walls come in at the close of the third mitosis they form two 

 tiers of cells with four cells in each tier. The cells of the upper tier 



