SKCT. I 



MORPHOLOGY 



Cell Division. — In the uninucleate cells of the higher plants cell 

 division and nuclear division are, generally, closely associated. The 

 supporting fibres of the spindle extending from pole to pole persist as 

 CONNECTING FIBRES between the developing daughter nuclei (Fig. 86, 

 9 v; Fig. 88, 12, 16), and their number is increased by the inter- 

 position of others (Fig. 86, 10). In consequence of this a barrel- 

 shaped figure, the phragmoplast, is formed, which either separates 

 entirely from the developing daughter nuclei, or remains in connection 

 with them by means of a peripheral sheath, the connecting utricle. 

 The first is the case in cells rich in cytoplasm, the latter when the 

 cells are more abundantly supplied with cell sap. At the same time 

 the connecting fibres become thickened (Fig. 86, 10) at the equatorial 

 plane, and the short rod-shaped thickenings form what is known as 

 the cell plate. In the case of cells rich in protoplasm or small in 

 diameter, the connecting fibres become more and more extended, and 



touch the cell wall at all points of 

 the equatorial plane (Fig. 86, 11). 

 The elements of the cell jilate unite 

 and form a cytoplasmic limiting layer, 

 which then splits into two. In the 

 plane of separation the new partition 

 wall is formed of cell-wall substance, 

 and thus simultaneously divides 

 the mother cell into two daughter 

 cells (Fig. 86, 12). If, however, the 

 mother cell has a large sap cavity, 

 the connecting utricle cannot at once 

 become so extended, and the partition 

 wall is then formed successively (Fig. 93). In that case, the partition 

 wall first commences to form at the point where the utricle is in 

 contact with the side walls of the mother cell (Fig. 93 A). The 

 protoplasm then detaches itself from the part of the new Avail in 

 contact with the wall of the mother cell, and moves gradually across 

 until the septum is completed (Fig. 93 ^ and C) ; the new wall is 

 thus built up by successive additions from the protoplasm. 



The connecting fibres of the spindle consist of kiaoplasm. The origin of the 

 cell-plate from swellings of these fibres indicates its kinoplasmatic nature also. By 

 the splitting of the cell-plate the limiting layers of the two sister cells are com- 

 pleted acro.ss the place of separation. The separation of the complex of connecting 

 fibres into two halves effects an equal division of the kinoplasm between the two 

 new cells. 



Fio. 93. — Tliree stages in the division of a 

 living cell of Epipactis jjffZwstris. (After 

 Tkeub, X 365.) 



In the Thallophytes, even in the case of uninucleate cells, the 

 partition wall is not formed within connecting fibres, but arises 

 either simultaneously from a previous!}' formed cytoplasmic plate, or 

 successively, by gradual projection inwards from the wall of the 

 mother cell. It was a division process of this kind (Figs. 94, 95) 



