300 BOTANICAL GAZETTE | APRIL 
tion. The author's investigations on this point are exceedingly interesting. 
There is one centrosome which lies in a depression beside the resting nucleus, 
The centrosome appears “ naked" in the living condition, no attraction sphere 
being seen around it. The author agrees with Hicker that the attraction ~ 
sphere is an artificial structure produced by plasmolytic contraction of the 
centrosome. While the nucleus is in the resting stage there are no radiations 
around the centrosome; but when nuclear division begins the centrosome 
passes out of the depression and becomes surrounded by exceedingly well 
defined radiations, which appear as definite in the living state as in fixed 
preparations or more so. There isa close relation between the centrosome 
and nucleus, which becomes apparent when the nucleus is forcibly removed 
from the cell. In this case the centrosome remains attached to the nucleus 
even if all the cytoplasm from both has been torn loose. The fact that the 
centrosomes, as in Surirella, can be seen plainly in living cells is a strong 
argument against the temporary organ hypothesis. The centrosome is @ 
kinetic center from which, at the beginning of nuclear division, activities pro- 
ceed out upon the nucleus and cytoplasm, which appear morphologically as 
radiations around the centrosome. When the radiations appear a new body 
arises in close proximity to the centrosome, which is the beginning (Anlage) 
of the central spindle. This y appears to come from the centrosome by 
division or budding, although the process was not observed. The central 
spindle body soon increases in size and begins to pass through a series of 
peculiar forms. It elongates and becomes sheaf shaped, and when the 
nuclear membrane has disappeared, it enters into the nucleus, and the 
chromatin segments arrange themselves about its equator and are then carried 
to the poles. The author has very carefully observed that the central spindle — 
body is not to be confounded with a nucleolus. Before the central spindle 
enters into the nucleus the centrosome begins to vanish. During the forma: 
tion of the daughter nuclei a centrosome appears at each end of the central 
spindle, and when the nucleus is about completed a centrosome lies in the 
nuclear depression at the central point of the cy SE radiations. At 
_ this stage nothing more is to be seen of the constricted ends of the spindle. 
= ir sublstanes i is wie esy wears into the centrosomes. The origin of 
2a not definitely determined. Either sec 
ice are formed at ~ two poles of the central spindle 
. by the original - goes to pieces, 
some is alwz at hand, the two dark  heanapherienl bodies which appeat — 
on both sides of the central s staal; may be formed by division of the original : 
: centrosome, and these t two bodies later become differentiated into new cen” 
or hi a _The whole nucleon: zand coll 
) pieces, or, since the original centro- 
