The Mechanism of Nuclear Division. 
BY 
W. LAWRENCE BALLS, M.A. 
Fellow of Si. John s College , Cambridge ; Botanist to the Khedivial Agricultural Society , Cairo ; 
Membre de P Inst it ut fgyptien. 
With Plate LIV and one Figure in the Text, 
Introduction. 1 
M ORE attention has been given by cytologists to the chromatic 
substances of the nucleus than to the achromatic substances, partly 
on account of the difficulty of observing the latter. 
Attention has been further attracted to the chromosomes by the 
discovery of numerical constancy, by their localization as the germ-plasm, 
and lately by Mendelian developments. The study of the achromatic 
structures has lagged behind, and our knowledge of their behaviour in the 
process of karyokinesis is consequently incomplete. 
We have no good evidence as to the way in which the spindle fibres 
are formed, nor of the changes which take place between the splitting of the 
spireme and their appearance. Many hypotheses have been advanced con¬ 
cerning the spindle fibres, but none of them hold out any hope of genera¬ 
lization. Botanical studies on these structures received a check by the 
disproof of Guignard’s work on the centrosome, and the artifact preparations 
obtained by other workers have made the cytologist very chary of publi¬ 
cation. 
1 Since this paper will presumably be read by professed cytologists, to whose ranks the writer 
cannot claim to belong, a word regarding the circumstances of its publication seems advisable, by 
way of apology. The observations arose during an examination of the sexual cytology of Egyptian 
cotton, made in 1905 as a preliminary to Mendelian research on this plant. They were continued 
for a year, and the present paper, in its present form, was written during the summer of 1906. The 
conclusions seemed so heterodox that publication was delayed till more evidence could be accumu¬ 
lated from other plants, such as Hibiscus spp ., which might be expected to show similar phenomena 
to those exhibited by Gossypium. Pressure of other work in Genetics and Physiology has prevented 
the acquisition of such supplementary evidence, and this four-year-old account is now being published 
in the hope that other botanists, better qualified than the writer, may find something of use in its 
pages, even if the generalization here advanced may not hold good. 
The substance of this paper was communicated to the Cairo Scientific Society early in 1906, and 
an abstract was read and published at the Dublin meeting of the British Association in 1908. 
[Annals of Botany, Vol. XXIV. No. XCVI. October, igio.] 
