Dixon — First Mitosis of Spore-mother-cells of Lilium. 7 



the Wo portions of the twisted chromosomes separate, and each by 

 itself forms a single V-shaped chromosome for the new nucleus. Two 

 different methods for this formation have been urged. Parmer^ 

 believed that each twisted chromosome bends on itself about the middle, 

 and at the point of bending becomes attached to the fibres of the 

 spindle. The fibres from one pole form connections with one of the 

 portions, those from the other pole with the other portion of the 

 chromosome. In this way each V-shaped daughter chromosome 

 really represents one complete and intact portion of the twisted 

 chromosome bent upon itself. In this view Parmer is followed by 

 Miss Sargant^ and Mottier.^ Undoubtedly such a bending, as Farmer 

 describes, may occasionally be seen, but I venture to think that it is 

 far from being the general rule. As Gregoire* suggests, it seems to 

 have become regarded as the normal form in order to explain the 

 general occurrence of V-shaped daughter chromosomes arising from the 

 division of the equatorial plate ; but as Gregoire also has pointed out, 

 these bent chromosomes in reality give rise to 4 V-shaped daughter 

 chromosomes, while the much more general unbent form gives rise to 

 the normal two V-shaped chromosomes. 



Although Gregoire in this respect differs from Farmer, he agrees 

 with the latter in regarding the division which takes place in the 

 equatorial plate as separating the two portions of the twisted chromo- 

 somes and distributing them to the daughter nuclei. He believes that 

 as they separate from one another they undergo a longitudinal fission, 

 and as they part from the equator the ends of these cleavage segments 

 nearest the equator diverge, and so the V-shaped chromosomes are 

 formed. 



This explanation, however, does not, I think, take into account the 

 manner in which the V-shaped daughter chromosomes actually part 

 asunder from one another in the equatorial plate. If Gregoire' s scheme 

 were accurate, it would seem that at the moment of separation the two 

 daughter chromosomes would often be laterally displaced one over the 

 other so as not to lie on the same meridian of the cell ; both limbs of 

 the upper V should lie to the left of those of the under, or vice versa. 

 This would appear to be the natural result from the formation of the 

 two limbs of each V-shaped daughter chromosome from one twisted 

 portion of the chromosome of the equatorial plate. Gregoire^ himseK 



^ Farmer and Moore. Anat. Anzeiger. Aug. 1895. 



2 Miss Sargant, Ann. of Bot. Sept., 1896. ^ Mottier Jahrb. f. wiss. Bot. 1897. 



* Gregoire, loc. cit. ^ Loo. cit., figs 17 and 20. 



