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1907] KI LD A HL— PRO EMBRYO OF PINUS LARICIO 105 



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fig, p. Figs. 6 and p show the fibers radiating from the nuclei to 

 the walls. The vertical walls in each tier are formed by the fibers from 

 the nuclei of their respective tiers, as is shown in fig, 8, As a rule the 

 cross wall is formed somewhat in advance of the vertical wall {figs. 



m 



4-9). Fig. 8 shows the cross walls completed, except at the edges, 

 while the vertical walls are still in an early stage of development; 

 this is also shown in fig, p. The cross walls are formed in the usual 

 way, each on its own spindle, as is shown in fig, 6. These walls, 

 therefore, are formed in connection with the first division of the four 

 nuclei. It might be said that the proembryo passes from the four- 

 nucleate stage to the eight-celled stage were it not for the fact that the 

 four nuclei farthest from the base of the egg are still freely exposed to 

 the egg mass. 



The very coarse granules gradually disappear, as shown in figs. 

 4-9^ while the deeply staining areas first seen in fig. 4 increase in 

 size until in figs. 8 and p they entirely surround the nuclei and extend 

 irregularly into the surrounding cytoplasm. 

 A The second division in the base of the egg, as a rule, takes place 



in the exposed tier {fig. 10)^ although it may take place in the basal 

 tier, as shown in fig, 11. The cross and vertical walls are formed 

 as in the previous division. 



The next and last division occurs in the basal tier {fig. 12), and, 

 so far as has been reported, it never takes place in either of the other 

 two tiers. This sequence of divisions is also reported by Hofmeister 

 (l) in Pinus Strohus and by Miyake (6) in Picea excelsa. Tlic last 

 division in the proembryo of Pinus Laricio is not always simultaneous 

 in the four nuclei, as has heretofore been reported; one section 

 showed two nuclei in metaphase and the other two in late telophase. 



The proembr}'o has now completed its development and consists 

 of three completely walled tiers of four cells each, and the tier of four 

 nuclei separated from each other by vertical walls but free toward 



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the egg mass. 



SUMMARY 



I, The cross walls in the proembryo of Pinus Laricio are formed 

 in the usual way, on cell plates formed on the spindles in the division 

 of the nuclei, and the first cross walls come in a little in advance of 

 the vertical walls. 



