Centrifugal Force upon the Cell ’ 327 
in intensity of the centrifugal force could be obtained without 
varying the speed of the motor h 
Cladophora. 
As Cladophora proved to be a suitable object for these 
experiments, and since the results in many respects were 
strikingly interesting and instructive, a detailed account of 
the behaviour of this plant may serve as an introduction to 
what follows, and also to give some idea of the phenomena 
discussed. 
Fresh growing specimens, with tolerably large cells, were 
always selected for study. 
Pieces of filaments about 2 or 2| centimetres long were 
fastened upon a slide under a cover-glass by means of gypsum. 
One end of the filaments only is enclosed in an edge of the 
cast so made that this edge projects a short distance under 
one side of the cover-glass and overlapping the latter to the 
same extent. By means of sealing-wax, small grains of sand 
were first glued to the opposite corners of that edge of the 
cover-glass enclosed in the cast : in this way the cover-glass 
is held firmly and steadily in the same position. A larger 
grain of sand is similarly glued to the slide over which the 
cast is made in order to prevent any movement of the latter 
from side to side, and a small rubber-band holds cast and 
slide securely together. The preparations thus constructed 
are packed securely in the cylinders with cotton, and enough 
water is added to cover the specimens. 
This method of preparation permits direct observation 
immediately upon removing the specimens from the centri- 
fugal machine, and at any subsequent time. 
1 The centrifugal force may be calculated according to the following formulae : 
47 x R (in metres) 47r 2 
— ■ — — } — = 4-024, a constant. 
gt L g ^ ^ 
R r , 
4-024 x - 2 = no. of g (gravity). 
R — radius expressed in metres. 
t = time in seconds of one revolution of the drum. 
