158 MR A. ANSTRUTHER LAWSON ON 
This attachment is undoubtedly brought about by the enveloping of each bivalent 
chromosome by the receding nuclear membrane. ‘This membrane, which is really the 
base of the drawn-out threads, upon being closely applied to the surface of each bivalent 
chromosome, furnishes each of these bodies with its own system of kinoplasm. 
No evidence was found to support the view that the contraction of the attached 
fibrils draws the daughter chromosomes to the poles of the spindle. Such fibrils may 
serve as guide lines, but take no active part in the movement. 
Taking all of the facts into consideration, | am forced to the conclusion that 
the achromatic spindle in vascular plants is simply an expression of a state of 
tension in the cytoplasm, and that this tension is caused in the first place by nuclear 
osmotic changes which create a condition where a limited amount of cytoplasm is 
obliged to occupy an increased cubical space. 
As a result of this investigation, I can no longer regard the achromatic figure as 
an active factor in mitosis. It seems to be nothing more than a passive effect of 
nuclear osmotic changes. 
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