20 
LABORATORY EXERCISES 
also note the centrosomes in the cytoplasm near the nucleus. In 
higher plants centrosomes do not appear.) 
II. Mitosis. Cells multiply by a process known as cell division 
or mitosis. Study the models or slides provided for the purpose of 
illustrating the various stages of this process. 
1. What is the first change in the nucleus? What happens soon 
to the ribbon-like chromatin strand? The segments of this strand 
are called chromosomes. 
2. Where do chromosomes tend to arrange themselves? What 
happens at the same time to the membrane surrounding the 
nucleus? 
3. When the chromosomes have become arranged in the center 
of the cell, observe the divisions in each. What structure appears 
at either side of the chromosomes? Describe this spindle. What 
successive changes occur in the location of the chromosomes? 
4. What becomes of the chromosomes when they have reached 
the poles, the points from which the spindle fibers radiate? What 
change is taking place during this process in the cell wall (or 
membrane)? 
5. How many chromosomes will each daughter cell have as 
compared with the number in the original cell? Why? Of what 
importance is this fact? 
(Note — Place cuttings of geraniums or some other house plant 
in water. See Exercise 28.) 
EXERCISE 22 
DIFFUSION 
Fill a tall, narrow glass jar with clear water. Into this drop a 
few large solid crystals of potassium permanganate. Allow this 
jar to remain undisturbed in a quiet place of uniform temperature 
for two or three days. Observe frequently. Note the distribution 
of the permanganate as indicated by the density of color. Where 
is the permanganate most abundant? Where is it least so? In 
what direction has it been possible for the molecules of the dis- 
