. The cell and protoplasm ... Cells; Protoplasm; Cytology; Cytoplasm. STRUCTURAL UNITS IN CELLULAR PHYSIOLOGY 203 3. Tliat the chromosomes in tlie region near the centromere are capable oL" liberat- ing material Avhich disaggregates the long particles in its immediate vicinity. 4. That there are progressive chemical changes of a cj^clical nature which first tend to lengthen and later to break up these long particles. The mechanism of cell division would then proceed as follows (Fig. 3). From. Fig. 3. Meclianism of cell division. the centrosome a wave of orientation would result first in a
. The cell and protoplasm ... Cells; Protoplasm; Cytology; Cytoplasm. STRUCTURAL UNITS IN CELLULAR PHYSIOLOGY 203 3. Tliat the chromosomes in tlie region near the centromere are capable oL" liberat- ing material Avhich disaggregates the long particles in its immediate vicinity. 4. That there are progressive chemical changes of a cj^clical nature which first tend to lengthen and later to break up these long particles. The mechanism of cell division would then proceed as follows (Fig. 3). From. Fig. 3. Meclianism of cell division. the centrosome a wave of orientation would result first in a physical aster (a). The di- vision of the centrosome, due to instability in the field of these forces, would next lead to the formation of a spindle (b). At the same time, the centromeres having divided, small negative spindles would be formed around each of them. These negative spin- dles would be then drawn into the equa- torial plane of orientation parallel to the main spindle (c). In cases where the main .spindle is not formed, subsidiary spindles would simply be arranged in parallel. As the elongation of the particle proceeds, both the positive and the negative spindles would grow in length, driving the now di- vided chromosomes farther and farther apart, and leaving an area of parallel ori- ented material between them (d). Finally, the long particles would break up into short ones and the process would pass into the next resting phase (e). The formation of a dividing cell wall would seem to be closely linked with the existence of the long particle field, as it tends to grow per- pendicular to the fiber direction. The evi- dence for tlie truth of this picture is still very scanty. The existence of a positive tactoid is, however, fairly safe, as it is marked in living cells by its birefringence. For the negative tactoid there is much less evidence; some photographs do, however, seem to show that the remaining fibers at anaphase seem to be located not on the lines joining t
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Keywords: ., bookauthoramericanassociation, bookcentury1900, booksubjectcells
