ANATOMY OF THE CELL. 29 
Essentially the same process occurs in other cases where the 
seements are less regular in shape and number than in Fritil- 
laria. ‘This is illustrated by Figs. 4-7, in Plate 15. 
During this time the spindle fibers retain their shape and 
size. About the time of the completion of the two nuclei, a 
little swelling appears near the middle point of each of these 
threads, so arranged as to form a plate through the equatorial 
plane, or the place formerly occupied by the nuclear plate. 
These swellings increase in size until they finally coalesce and 
form what Strasburger has named the cell plate. This plate is 
intimately connected with the formation of the cellulose wall 
which soon afterward appears, dividing the cell into two 
daughter-cells. 
It has been found very difficult to ascertain the exact 
numerical relations between the spindle fibers and the seg- 
ments. It is possible, however, that there are as many fibers 
as segments, and the latter are supposed to move along the 
fibers to the poles. There are also some grounds for supposing 
that the substance composing the spindle fibers is not a part of 
the original nucleus, but of the cytoplasm of the cell. For 
example, it is said that these fibers never appear until after the 
membrane of the nucleus is dissolved, and that previous to 
the disappearance of this membrane, the nuclear segments are 
the only differentiated structures found in the substance of the 
nucleus. 
5. Plastids. 
Plastids are of three kinds, chloro-, chromo-, and leuco- 
plastids. The first includes all structures which contain chloro- 
phyll or the green coloring matter of plants. This is a pigment 
found in all classes of plants except fungi, and generally con- 
nected with some certain portion of the protoplasm. In some 
of the low algae, however, it is equally distributed through 
the whole mass of protoplasm. It is also claimed that it is 
