126 MARGARET C. FERGUSON 



Every transitional form may be presented during the metakinesis 

 between a multipolar diarch spindle, which fills the entire breadth 

 of the nucleus, and a slender bipolar spindle, such as is shown 

 in fig. 253, b. As the halves of each chromosome separate at 

 the point where the spindle-fibers are attached, the longitudinal 

 splitting of the segments becomes evident throughout the entire 

 length of the chromosomes (fig. 253, b.) 



The Development 0/ Cell-walls. — During mitosis, the deeply 

 staining substance surrounding 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 (figs. 253, b, and 254, b). 

 Blackman describes the formation of cell-walls about the four 

 nuclei at the base of the archegonium, and Coulter and Cham- 

 berlain state that cross-walls separating these nuclei, but leav- 

 ing them exposed above, arise when the four nuclei have 

 arranged themselves at the base of the oosphere, and are under- 

 going division. In the five species of pines which I have studied 

 cell-walls 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 transformation of this sub- 

 stance. The process seems to be very similar to that described 

 by Farmer and Williams ('98) in Fitciis. Mottier ('00) inclines 

 to the view that the cell-plate is deposited in the form of a homo- 

 geneous fluid, the kinoplasm, even though its presence cannot 

 be demonstrated, being the active agent in its deposition. The 

 substance which is cast out, or passes out, from the region of 

 the eight nuclei in the formation of cell-walls at the base of the 

 oosphere in Pinus, has the appearance at times of a homogene- 

 ous, deeply staining fluid, in which numerous irregular granules 

 are imbedded ; but there is never any evidence of its being purely 

 fluid in nature. It seems very probable that the large granules 

 cast out from the cytoplasm surrounding these nuclei at this 

 time are similar to the smaller granules deposited at the cell- 



