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I. W. BAILEY 
cell. In his second type, the nucleus lies near one wall and the daughter 
nuclei and ''fibrillar-complex" migrate to the opposite side during cyto- 
kinesis. Strasburger described a third type, in which the daughter nuclei 
remain on one side of the cell and the " fibrillar-complex " crosses it. Schiir- 
hoff found a fourth type, in large cells having centrally located nuclei and 
small spindles. It differs from the preceding types in that "mit der Neu- 
bildung der peripheren Cytoplasmafaden geht die Auflosung der zentralen 
Strahlungen Hand in Hand." ^ In other words, a ring or halo of kinoplasm 
is formed such as occurs in cambial initials during incipient stages of cyto- 
kinesis. 
A comparative study of cell plate formation in different somatic tissues, 
and in cells of different shapes and sizes, suggests that the various types of 
phenomena, described by Treub, Strasburger, Schiirhoff, and the writer, 
are but different phases or stages of a single general or fundamental type 
of cytokinesis. The particular expressions of the phenomenon which may 
occur in any given cell are dependent upon its dimensions, its plane of 
division, and the size and location of the nucleus. Thus, in very small, 
isodiametric cells having a large, centrally located nucleus, the cell plate 
quickly intersects the walls of the cell without any extensive lateral en- 
largement of the central spindle. In larger cells with small nuclei, there is 
sufficient room for the process of cytokinesis to reach the halo or frame 
stage before the cell plate intersects the sides of the cell. However, only 
in elongated or much flattened elements is it possible for the phenomenon 
of cell plate formation to pass through the spindle, disk, halo, and frame 
stages, and finally to form two entirely separate aggregations of kinoplasmic 
fibrillae, kinoplasmasomes. 
All five types of cytokinesis may be found in the cambium. Treub's 
first type occurs in ray initials (fig. 31) and in transversely dividing fusiform 
initials (figs. 29, 49). Schiirhoff 's type also is present in certain ray initials 
(fig. 32) and transversely dividing fusiform initials (fig. 48). Although the 
nuclei are centrally located under normal conditions, I have found them in 
a lateral position in Sequoia, in fusiform initials which were dividing to 
form callus. During cytokinesis the daughter nuclei remained on one side 
of the cell, as in Strasburger's preparations (figs. 45, 46), or one or both of 
them migrated across the cell, as in Treub's second type of cytokinesis 
(fig. 52). 
Significance of Cytokinesis in the Cambium 
The formation of the cell plate in cambial initials promises to be signifi- 
cant in the discussion of a number of fundamental cytological and physio- 
logical problems. 
Strasburger's (1875, 1880, 1882) suggestion that spindle fibers are of 
cytoplasmic origin and his conclusion that the cell plate originates in swell- 
^ A phenomenon previously noted by Went (1887). 
