76 
LABORATORY EXERCISES 
EXERCISE 75 
ANIMAL REACTIONS 
I. Reaction to Light. Collect land sow bugs (Porce^^^o). (Look 
for these in moist, dark situations, such as the under side of boards 
which lie on the ground.) Place a number in a dish which has been 
half covered with black paper. Place the dish in the light. Leave 
undisturbed until the animals are resting. Then note the distri¬ 
bution of the animals. Record. Repeat the experiment several 
times. Average the results. To what stimulus have these animals 
responded? In what way? An animabs reaction to light is known 
as phototaxis. 
II. Reaction to Moisture. Use land sow bugs. Cover the 
bottom of a pan, one half with rather moist soil and the other half 
with dry soil. (Use the same kind of soil for each half. Why?) 
Place the sow bugs near the center. Cover to exclude the light 
and allow the pan to remain undisturbed for some time. Then un¬ 
cover and note the distribution of the enclosed animals. Record. 
Repeat a number of times. Average the results. To what stimulus 
have the animals responded? In what way? An animal’s reaction 
to moisture is known as hydrotaxis. 
EXERCISE 76 
PLANT REACTIONS 
I. Reaction to Light. 
1. Place a box or pot in which young oat seedlings are begin¬ 
ning to appear above the soil, a short distance inside a sunny 
window. Leave undisturbed for a few days. Then note the posi¬ 
tion of the plants with relation to the Hght. Reverse the position 
of the box. Note any changes in the position of the plants. 
2. Keep oat seedlings in darkness until about an inch high. 
Then expose for two minutes to sunlight which enters from one 
side only. Leave in darkness for a number of hours. Examine at 
the end of the period for any change in the position of the plants. 
