Balls .— The Mechanism of Nuclear Division . 665 
another plant. Fixation good. x 7 °°* e P-t epidermis; p 1 , p 2 , parietals; m.c.n ., microspore 
mother-cell nucleus ; iap., tapetum. 
Fig. 2. Synapsis. Younger anther, parietals and tapetum unaltered, but mother-cell nucleus 
already in synapsis. x 450. 
Fig. 3. Portion of spireme and nucleolus of synapsis, slightly later. Nucleolus scarcely 
shrunken, thread definitely split, chromatic areas fairly evenly spaced, and bisected. x 1,100. 
Fig. 4. Very late spireme, showing two fully differentiated chromosomes, each of four units, 
split thread uniting them; nucleolus nearly gone, but still continuous with thread, x 1,100. 
Fig. 5. The cluster of chromosomes at one side of the mother-cell nucleus, in prophase of first 
division. The halves of the spireme thread are conspicuous objects. The chromosome on the 
extreme left was seen clearly to be connected on either side to the ‘ thread-rings ’, by means of short 
fibres, x 900. 
Fig. 6. Late prophase of same division. Spindle fibres connecting chromosomes to thread- 
rings, but not yet drawn taut in all cases, x 1,300. 
Fig. 7. Metaphase of first division, separation of chromosomes commencing. Section slightly 
oblique to spindle, showing insertion of bunched spindle fibres in thread-rings at pole, x 1,100. 
Fig. 8. The same, in another cell, showing spindle fibres below which have not yet been drawn 
up into the polar group. Semi-diagrammatic, x 1,500 about. 
Fig. 9. One of the first pair of daughter-nuclei in prophase of second division. The arrow 
points to the other daughter-nucleus. Note that the loops of the thread-ring are double, approxi¬ 
mately superposed (indicating origin by splitting) and unbroken on the side of the arrow. They can 
be followed throughout their length except on the polar side, where a portion is hidden by the 
chromosomes, x 1,000. (Spindle fibres omitted.) 
Fig. 10. Later prophase of same, showing rings very clearly. Semi-diagrammatic, x 1,500. 
Figs. 11, 12, and 13. Division of vegetative cells in root-tip. 
Fig. 11. Polar view of prophase. Nucleolus stellate, slung by bridles of linin to one of the 
thread-rings. Peripheral chromosomes, connected to both rings by incipient spindle fibres, x 1,500* 
Fig. 12. Side view of spindle in metaphase, showing rings at either end, with spindle fibres 
ending upon them, x 1,100. 
Fig. 13. A single thread-ring in metaphase, showing the plasmosome in this case as a simple 
dilatation of the ring, x 1,500. 
