353 
Centrifugal Force upon the Cell. 
that £ when the ovary of a lobster is killed, the nucleoli of all 
the nuclei are found in contact with that part of the nuclear 
membrane which was the lowest at the moment of killing ’ 
( 1 . c., Fig. 22), and that c the weight of the nucleolus is 
relatively so great as sometimes to cause a depression in 
the part of the nuclear membrane upon which it rests ’ 
( 1 . c., Fig. 33). 
Strong centrifugal force reveals a series of phenomena 
relative to the specific gravity of the nucleolus, to which we 
shall now direct our attention. 
In the smaller and densely filled embryonic cells of the 
root-tip, very little change is to be noticed ; but farther 
back, where the cells have elongated somewhat, a marked 
difference is at once apparent. In those nuclei in which 
a displacement is plainly perceptible, the nucleolus lies in 
contact with that part of the membrane toward which the 
centrifugal force has been directed. (As in the case of the cell, 
this part will be spoken of as the lower side.) Not only the 
nucleolus, but much of the nuclear reticulum is displaced 
along with the former (Fig. 12). In cases like this the nucleolus, 
together with a portion of the threadwork, causes a decided 
depression in the nuclear membrane. To what extent the 
reticulum is pulled along by the heavy nucleolus cannot be 
stated with certainty. 
From the displaced mass of reticulum there extend back 
to various points in the nuclear membrane many linin- 
strands (Fig. j 2). That part of the nuclear membrane 
directly opposite the displaced mass to which these linin- 
threads extend is depressed or sunk in. In a great many 
nuclei presenting a similar orientation of their contents, a 
similar indentation is present. It is not, therefore, due to 
shrinkage, and the fact indicates strongly that the linin-thread 
at certain points is pretty firmly attached to the nuclear 
membrane. 
The nucleolus is often only heavy enough to cause a slight 
depression at the lower side as in Fig. 12, but frequently this 
depression is augmented to a protuberance or beak equalling 
