146 Mk A. ANSTRUTHER LAWSON ON 
of the fibrils, but, as seen in fig. 8, the lateral surface of each chromosome is furnished 
with many more fibrils than the end surface, and for this reason the disposition of the 
fibrils is not symmetrical. Also, the close juxtaposition of the chromosomes would aid 
in the prevention of symmetry. This unsymmetrical arrangement, however, is of very 
short duration. The greater surface from which project the larger number of fibrils 
apparently dominates the direction of the lines of tension, and in this readjustment the 
bivalent chromosomes become less crowded and each one becomes suspended between 
two sheaves of fibrils, as shown in fig. 9. 
The state of tension set up in the cytoplasm by the gradual diminution and final 
vanishing of the nuclear vacuole now finds an expression in two conical-shaped sheaves 
of kinoplasmic threads which appear on opposite sides of each bivalent chromosome, 
so that, as shown in fig. 9, each of these bodies is provided with an independent 
miniature spindle, and these lie parallel to one another. Now, as the surfaces which 
form the base of attachment for the fibrils are equal, so the two sheaves on the opposite 
sides of each chromosome are also equal, and the chromosome is thus suspended at the 
equator. Applying this to all five chromosomes, and taking into consideration the 
more or less parallel arrangement of the main lines of tension, we have here an exceed- 
ingly suggestive explanation for the organisation of the equatorial plate. But in this 
connection it should be remembered that we know little or nothing in regard to the 
problem of cell polarity in the vascular plants, and the plane occupied by the chromo- 
somes during the metaphase is too closely involved in this problem to justify my 
offering the above as an adequate explanation. I have no hesitation, however, in 
expressing my belief that the osmotic surfaces enveloping each chromosome are 
determining factors in the suspension of these bodies between two sets of fibril sheaves 
of fairly equal size. 
From a study of dividing cells in Disporum and other types which I will mention 
later, no evidence was found to support the view, held by Strasburger and others, 
that the daughter chromosomes are drawn to the poles by the contraction of the spindle 
fibrils. That these fibrils shorten and thicken with the movement of the chromosomes 
towards the poles is no doubt quite true, but this is not sufficient proof that they are 
actually engaged in the pulling of these bodies to opposite ends of the spindle. I believe 
that this shortening and thickening is due to the relaxing of the tension in these 
fibrils as the chromosomes move to the poles, and the fibrils merely act as guide lines 
with no pulling force. Although the tension in the fibrils between the daughter 
chromosomes and the poles of the spindle is thus relaxed, as shown in fig. 10, the 
tension in the cytoplasm as a whole has not been relaxed, for we see new lines of 
tension expressed in the fibrils stretching between the pairs of daughter chromosomes. 
This is quite clear in figs. 10 and 11. There has merely been a shifting of the lines of 
tension caused by the movement of the chromosomes to the poles. It should be noted 
in passing that the daughter chromosomes move beyond the actual poles of the spindle. 
This feature was observed not only in Disporwm, but in many other types, and it 
