No. 460.] 



STUDIES ON PLANT CELL. V. 



231 



The fibrillae organize a multipolar spindle which is very vari- 

 able in form, sometimes with broad poles of a multipolar diarch 

 (Fig. 17, d) and at other times almost as pointed as-in-a typical 

 bipolar spindle (Fig. 17, e). There are, of course, no centro- 

 somes and the entire spindle in essentially of intranuclear origin. 

 The history of its development recalls Miss Williams' account 

 of the spindle in the pollen mother-cell of Passiflora (Sec. Ill, 

 Amer. Nat., vol. 38, p. 738, 1904). During spindle formation 

 the spirems of the sperm and egg nuclei can be readily distin- 

 guished as was described by Blackmail ('98) and Chamberlain 



FIG. 17. Fertilization in Pinus stratus, a, conjugating gamete nuclei; b, the gamete nuclei 

 still separated, with nuclear membranes distinct, the maternal and paternal chromatin in 

 two spirems ; c, the nuclear membranes have disappeared and the two spirems lie close 

 together surrounded by the fibrillse which will organize the first segmentation spindle; d, 

 prophase of the first segmentation spindle, of the multipolar diarch type, paternal and 

 maternal spirems still distinct ; e, metaphase of first segmentation mitosis, maternal and 

 paternal chromosomes now indistinguishable, beginning to split in the middle region (after 

 Ferguson, :o4). 



('99), but after the two sets of chromosomes are formed (twelve 

 of each) the latter are brought so closely together at metaphase 

 of mitosis that the paternal and maternal cannot be separated. 

 All of the chromosomes are exactly alike and there is nothing in 

 the form or size to distinguish one from another as certain 



