146 
Charles E. Allen 
Soon the tkickenings at the opposite ends of each fiber seem to move 
toward one another and to meet in the equatorial region, leaving the 
ends thin ; the spindle now (Fig. 61) consists of three zones, a dark one 
in the middle separated by two lighter zones from the respective daughter 
nuclei. The darker appearance of the equatorial zone is at this time 
somewhat aecentuated by a greater density of the apparently undiffer- 
entiated cytoplasm in that region; and in preparations stained with 
iron-alum haematoxylin and Congo red, this interfilar cytoplasm shows 
a reddish stain. As Congo red is taken up readily by the walls of tliese 
cells, there seems to be no doubt that the red-staining substance here 
is of the same nature as the orange-staining cytoplasm found by Tbiber- 
lake at the same stage in the equatorial zone in dividing cells of Allium, 
and interpreted by him as due to the presence in this region of a carbo- 
hydrate material destined for use in the construction of the future cell wall. 
While the spindle is in the condition last described (Fig. 61), the 
beginnings of a cell plate appear in the form of minute swellings at the 
centers of the fibers — at first, usually, of some of those in the central 
part of the spindle. Figure 57, Plate VII, represents a cell in which afew 
such swellings (somewhat larger in this instance than usual) appeared 
considerably earlier, before the shortening of the fibers and the differentia- 
tion of the spindle zones; but this was the only such case observed. The 
processes of nuclear reconstruction and of cell plate formation do not in 
different cases always go on at the same relative rate; for example, the 
chromosomes in the nuclei of Figure 60, Plate VIII, are still short, thick 
and distinct, while in the cell shown in Figure 61, the nuclei have con- 
siderably expanded and the chromosomes have elongated and formed 
daughter spirems; on the otherhand, cell plate formation is plainly mueh 
further advanced in the former figure than in the latter. 
The equatorial swellings increase in number and, following the same 
course that has often been described for the higher plants, fuse into a 
plate, at first only in the central part of the cell (Fig. 60); then, by the 
development of swellings on the fibers nearer the peripherv, the formation 
of fibers further outward, and the equatorial swelling of these later-formed 
fibers (Figs. 62 — 64), the cell plate is gradually extended until its periphery 
meets the plasma membrane of the mother cell (Fig. 65). 
"Wilde the plate is under construction, the spindle fibers gradually 
disappear (Figs. 62 — 65). It is in the central part of the cell, where the 
plate is oldest, that a lessening in the amount of fibrous material is first 
noticeable. Usually the part of each fiber which persists longest is its 
central portion (see especially Fig. 62), an observation which harmonizes 
