THE LIVING CELL 49 
daughter chromosomes form a dense compact knot. A cell 
membrane (ced/ plate), composed of material contributed largely 
through the shrinking of the spindle fibers, is now formed 
through the middle of the spindle. This soon splits to form 
a thin vacuole lying between the two membranes (the plasma 
membranes). Presently there appears within the vacuole and 
between the membranes a substance com- 
posed chiefly of pectose (and represent- 
ing the primary cell wall) which later, by 
union with mineral substances, chiefly cal- 
cium, becomes the middle lamella. On either 
side of this deposit the plasma membranes 
form a cellulose membrane. The flattened 
vacuole extends toward the periphery and 
ultimately a complete cell wall is formed. 
The dense compact knots of chrom- 
osomes, at the poles of the spindle, that are to 
form the daughter-nuclei, now begin to 
expand and clear mesh-like spaces to appear 
between the expanding threads. As this 
process advances the chromosome substance 
becomes distributed through the nuclear 
cavity. It is soon possible to distinguish the 
chromatin from the linin. Eventually an 
irregular network of linin carrying chromatin 
granules is formed through the area of the 
nucleus. A nuclear membrane also is formed 
and the nucleolus reappears. ‘The spindle fibers 
disappear. The daughter-nuclei increase in 
size and each daughter-cell formed by this 
process now assumes the resting stage. 
The process of mitosis may 
phases and each of these briefly 
1. PropHase.—Construction 
spireme. 
B 
eae 
Pe 
Mm 
Cc 
Fic. 26.—Enlarged 
views of spindle fibers 
and cell-plate formation. 
A, swellings appearing 
on the fibers. 3B, lateral 
union of the swellings, 
forming a continuous cell 
plate. C, splitting of 
the cell plate into two 
plasma membranes. D, 
a cell wall is secreted be- 
tween the new plasma 
membranes of the 
daughter cells. (From 
“4 Textbook of General 
Botany” by Smith, Overton 
et al., Macmillan Co. 
Publishers.) 
a 
be divided into four stages or 
summarized, as follows: 
of the chromatic thread or 
Transverse segmentation of spireme into chromosomes 
and their longitudinal splitting into double chromosomes. Dis- 
appearance of the nucleolus or nucleoli. 
plasmic caps and spindle. 
Formation of the cyto- 
Disappearance of nuclear membrane. 
