FOR WAGGONER’S BIOLOGY 77 
To what stimulus are the plants responding? This reaction is 
called phototropism. 
II. Reaction to Gravity. Obtain the stems of large growing 
grasses. From these cut sections in such a way as to include two 
nodes and an internode in each. Place these sections in moist 
earth in a flower pot. See that they stand in a vertical position 
when the pot is upright. When prepared, turn the pot on its side. 
Leave undisturbed for twenty-four hours or longer. Observe at 
the end of this period. Where in a grass stem does growth occur? 
(See Waggoner, Page 15.) To what stimulus has the stem re¬ 
sponded? This reaction is called geotropism. 
EXERCISE 77 
THE SUNFISH 
Obtain a number of living sunflshes and keep them in an 
aquarium in the laboratory. Observe them very frequently. 
I. Where were the fish obtained? In what kind of water, shal¬ 
low or deep, still or running, clear or cloudy, were they found? 
II. What is the position of the fish in the water? Note the shape 
of the body. Compare the body in length, width, and depth. 
Note the covering of the body. To what may the arrangement of 
the scales be compared? What makes holding the fish in the hand 
a difficult matter? How do the shape of the body and the slimy 
coating adapt a fish for its movement through the water? Note 
the fins. How many paired fins do you find? The anterior ones 
are the pectoral fins and the posterior, the pelvic fins. These fins 
correspond to the pg^ired limbs of the higher vertebrates. Of the 
unpaired fins, the one in the median dorsal line is the dorsal fin* 
the one in the median ventral line, the anal fin; and the one at the 
posterior end, the tail or caudal fin. Which are used chiefly for 
propelling the fish through the water? Which are used chiefly for 
maintaining its balance? Note the structure of the fins. They are 
supported by fin rays and hard sharp spines. Compare the size 
