CELL DIVISION BY FURROWING IN MAGNOLIA 38 1 
as they are formed. During this division of the cell there is no indi- 
cation whatsoever of an equatorial differentiation in the spindle, nor 
does such occur immediately after the heterotypic nuclear division. 
There is considerable resemblance between this particular mode of 
cytokinesis and the typical division of animal cells, except that it is 
quadripartition and not bipartition. There are also no centrosomes in 
these plant cells, unless the work of Guignard can be taken as conclusive. 
The conditions under which these pollen mother cells are formed are 
not unHke those of such animal cells as eggs, etc., but are quite different 
from those of most cells of higher plants. These cells are free-floating 
in the liquid of the anther instead of being in a compact tissue. Beer 
(3) considers that the walls of these mother cells are composed of 
pectose, which swells in water, becoming soft and gelatinous instead 
of being relatively rigid and non-elastic as are cellulose walls. Finally 
they assume a spherical shape instead of being pressed into parallelo- 
pipeds and other flat-faced forms by mutual pressure, as occurs in 
root tips and other parts of higher plants. This similarity in the 
conditions which surround the pollen mother cells and many animal 
cells led the writer to conclude that these conditions have some physico- 
chemical effect in determining the type of cell division and that they 
might explain the resemblance of the pollen mother cells to the animal 
cells in this regard and their departure from the mode of cell division 
characteristic of the cells of most higher plants. 
Material and Methods 
The present study is based upon cultivated varieties of Magnolia 
growing at Cinchona Station on the island of Jamaica. Acknowledg- 
ments are due Columbia University for the William Bayard Cutting 
Traveling Fellowship, which made possible the collection of this 
material. The writer desires also to express his appreciation to Pro- 
fessor R. A. Harper, who offered many helpful suggestions during the 
prosecution of this work. 
The methods employed are the same as were used in the writer's 
previous investigation (6). Flemming's strong chromic-acetic-osmic 
solution was used in fixation and his safranin-gentian violet-orange 
G combination was the stain employed. Living cells were also studied, 
especially those of Magnolia tripetala. 
