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I. W. BAILEY 
the equatorial region of the spindle is shown in figure 30; but a discussion 
of the finer details of cell plate formation is reserved for a subsequent paper. 
The width of the kinoplasmasomes closely approximates that of the central 
spindle. In other words, broad kinoplasmasomes tend to occur in cells 
having large karyokinetic figures (figs. 27, 29) and narrower ones in elements 
having smaller spindles (figs. 17, 18, 19, and 20; figs. 25, 24, and 23, and 
figs. 31 and 32). 
The phragmoplasts develop along straight lines or curves depending upon 
the orientation of the karyokinetic figure and the plane in which the initial 
is dividing. In longitudinally dividing fusiform initials, in which the polar 
axis of the karyokinetic figure is transverse (fig. 25), the kinoplasmasomes 
move toward the ends of the protoplast along its longitudinal axis (figs. 
23 and 24). When the mitotic figure occupies a diagonal position (fig. 17), 
the phragmoplast, during its earlier stages, curves toward the center of the 
protoplast avoiding the tangential facets of the cell (figs. 18, 19), and subse- 
quently straightens out as shown in figures 20 and 21. In obliquely divid- 
ing cells having diagonally oriented division figures, either the phragmo- 
plast develops in a single plane (figs. 27, 51, and 52), or the kinoplasmasomes 
meander more or less, forming undulating or curved partitions (fig. 54). 
In the formation of new ray initials, which are carved out of fusiform initials, 
both kinoplasmasomes may, in certain cases, curve toward and intersect 
the same radial surface of the cell. 
Thompson (19 17) is of the opinion that Errera's (Plateau's) law of 
minimal area is not invalidated by the occurrence of oblique or curved 
partitions provided these membranes are sigmoid and intersect the older 
walls at right angles. De Wildeman (1893) found that in certain cells the 
polar axis of the division figure shifts to a diagonal position previous to the 
formation of the cell plate, which curves during its development so as to 
intersect the sides of the cell at right angles. That all diagonal partitions 
do not develop in this manner is indicated very clearly by the phenomena in 
the cambium. The writer (1920(2) has shown that the kinoplasmasomes, 
cell plates, and young membranes intersect the sides of the cell at varying 
degrees of acuteness, as well as at right angles. This suggests, of course, 
that in dealing with cytokinesis we are not concerned with protoplasm in 
liquid or semi-liquid phases. In other words, cellular membranes, at the 
moment of their formation, frequently do not assume the forms which 
would be assumed, under similar conditions, by liquid films destitute of 
weight (Plateau). 
Nucleoli 
The cambium of Coniferae appears to be an unusually favorable medium 
for the study of the structure and function of nucleoli, which are unusually 
large and conspicuous in most representatives of the family (Pis. XXVI, 
XXVII). In Pinus Strohus they vary greatly in size, shape, and number in 
different initials (figs, i, 10, 14, 33). They are clearly visible during the 
