Nuclear Division in the Hepaticae . 513 
to a transference of substance from one to the other, although 
this transference may take place in various degrees. Many 
other forms have been described and figured, especially by 
zoologists, which lend support to this view, and on the botani- 
cal side I may cite the observation of Strasburger on the 
embryo-sac of Galanthus \ in which he describes and figures 
the fragmented nucleolus lying along the young chromosomes 
within the nucleus. I have myself repeated this observation 
on the snowdrop, and have obtained quite similar results. 
But in attributing a nutritive function to the nucleolus 
I have left untouched the question as to what role (if any) is 
played by the other substances of which this enigmatical body 
is composed. Professor Strasburger has recently suggested 2 
that the nucleolus is concerned in an important way in the 
formation of the intra-nuclear part of the achromatic spindle. 
This may well be the case, at any rate there can hardly be 
any doubt but that a considerable part of perhaps all normal 
spindles is differentiated from substances within the nucleus ; 
and of course it must be so in those cases in which, as in 
Ascaris megalocephala , var. univalens , the whole spindle is 
intra-nuclear. I confess, however, that I feel sceptical as to 
the possibility, or even the a priori necessity, of deriving it 
from any one constituent of the cell, which one could regard 
as set apart to provide a ‘spindle-forming’ substance. It 
seems to me to be somewhat difficult to regard the spindle as 
a growing, organized structure at all, in the morphological 
sense of the term. I venture to think that the facts hardly 
warrant us in saying more than that the spindle-fibres are the 
visible expression of strains (and perhaps stresses) within the 
protoplasm. This protoplasm consists of, or at least includes, 
an extremely heterogeneous assemblage of substances which 
vary amongst themselves very much in such physical charac- 
ters as cohesion, viscidity, extensibility, elasticity, and the like. 
If the kinetic centres are really active existences, and there 
seems no reason to doubt this, then such c lines of force ’ as 
1 Strasburger, Die Controversen, p. 23. 
2 Strasburger, Karyokinetische Probleme. Pringsh. Jahrb., Bd. XXVII, Heft 1. 
