ago 



MORPHOLOGY OF GYMNOSPERMS 



The next division may occur in either tier, but usually in the upper 

 (open) one, resulting in three tiers of cells, two of which are inclosed 

 by walls. Still another division, usually in the lowest tier (fig. 347), 

 results in four tiers, and with this division the proembryo is com- 



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Figs. 350-352. — Pinus Laricio: three stages in the formation of the proembryo; 

 fig. 350, four nuclei (two shown) at base of fertilized egg, showing the fibers which had 

 been mistaken for a wall; X225; fig. 351, division of the nuclei shown in previous 

 figure, indicating that no wall is formed at the four-nucleate stage; X355; fig. 352, 

 late telophase of the mitosis the anaphase of which is shown in the previous figure; 

 the transverse walls are nearly complete and the vertical walls, formed on the radiating 

 fibers which are already becoming conspicuous in fig. 351, are developing; X350. — 

 After Miss Kildahl (129). 



plete (fig. 348). It consists, therefore, of twelve walled cells and 

 four open ones, arranged in four uniform tiers of four cells each. The 

 functions of the tiers are definitely distributed; the lowest forming 

 the embryo proper, the tier next above elongating to form the suspen- 

 sor, and the third walled tier constituting the so-called "rosette," 



