1900] THE CELL PLATE IN HIGHER PLANTS 165 
they fuse into a cell plate is to be accepted. In the splitting of 
the chromatin thread we may easily imagine the process taking 
place by constriction, but in the case of a continuous layer of 
protoplasm like the cell plate such a process would be impos- 
sible. The more so when we remember, as my figures show, 
that the splitting begins in the central portion and extends out- 
ward. 
The change in position of the cell plate during its growth is 
shown by figs. r2 and 27. The explanation of such a change is 
not obvious. The figures show that the nuclei do not move 
with the cell plate. Whether the cell plate ever changes from a 
true diagonal to a transverse plane I was unable to determine. 
The figures show only those cases where the plane in which the 
cell plate was first formed was not a true diagonal. Nemec” 
has shown that the position and form of the young spindle can 
be determined to some extent by means of pressure or tension 
exerted upon the tissues in which the dividing cells occur. It 
, Possible in these cases that the conditions of pressure or ten- 
‘ion upon the single cells have so changed by growth of some 
of the surrounding cells of the tissue as to bring about the 
change in position of the cell plate. The most obvious signif- 
ase of the shifting of the cell plate is that the original 
Pesition of the spindle cannot always be taken to determine 
accurately the ultimate plane of division of the cell. 
CONCLUSIONS. 
1. The most obvious and at the same time most important 
usin to be derived from the foregoing observations is 
ee the division of the cell body is due to the activity of the 
ies of hs cell. The splitting of the cell plate, OF at 
plants i: differentiation into separate layers, is in the higher 
not nae ey act in the division of the cell body, for it is 
Separatio such a differentiation has taken place that sea is a 
tinct at Be protoplasm of the mother cell into two dis- 
Parts. That the cell plate is kinoplasmic has already been 
— + Zelitheilung bei Solanum tuberosum. Flora 86: 214. 1899. 
