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1907] KILDAHL—PROEMBRYO OF PINUS LARICIO 103 



determine exactly what part the fibers play in the formation of these 

 walls, but of their connection with them there can be no doubt. 



The next work on Pinus was that of Chamberlain (4), who 

 describes the four nuclei in moving toward the base of the egg as 

 being invested by strong fibers which are directed tangcntially. 

 "Upon reaching the base of the oospore the four nuclei arrange 

 themselves in a plane and become ensheathed by fibers derived from 

 the nuclear membrane. Two walls are then formed at right angles 

 I to each other and to the base of the spore, each nucleus thus being 



separated from the others, but freely exposed to the general cyto- 

 plasm of the spore." He quotes Blackman (3) as thinking that 

 these fibers have some intimate connection with the formation of the 

 walls, and thinks that the appearance of these first incomplete walls 

 is quite apart from nuclear division. 



In 1904 Miss Ferguson (5) stated that *'after attaining full 

 size, the four nuclei pass to the base of the oosphere." ^' During their 

 descent many fibers arise in the cytoplasm surrounding the nuclei," 

 and she quotes Blackman as suggesting a relation between these 

 fibers and the walls that arise later, but says that she finds no con- 

 nection between the two. In regard to the formation of the first walls 

 she says: ''During mitosis the deeply staining substance surround- 

 ing these nuclei condenses into large, irregular masses at the periphery 

 of the nucleus. When the eight nuclei are formed this deeply staining 

 material collects about them and extends in irregular strands into the 

 cytoplasm. Each nucleus is now surrounded by its own cytoplasm, 

 though no cell-walls have yet been laid down/^ Further, she says: 

 ''In the five species of pines which I have studied, cell-wails do not 

 arise until after eight nuclei have been formed. The deeply staining 

 ^ cytoplasmic substance appears to be repelled from all sides of these 



] nuclei and is deposited in lines which indicate the position of the future 



cell-walls; the cell-membranes appear to arise by a direct trans- 

 formation of this substance." 



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DEVELOPMENT OP WALLS 



The material for the following study of the development of walls 

 in the proembrj-o of Pinus Larlcio was collected during the summers 

 of 1905 and 1906. It was taken from different trees and localities. 



V 







