Angles of Inclination. 317 
Alternation at 90° and ioo°. — In this test the curves in the roots 
of Lupinus albus came more slowly than in those of the preceding ex- 
periment, though the temperature here was 24° and there 22-5°. This 
would indicate that the stimulations on the opposite sides of the roots 
were more nearly equal. The result shows unmistakably that the position 
at 90° gives a stronger effect than at ioo°. The plants were placed first 
in the position with their axes inclined ioo° from the position of stable 
equilibrium, thus giving probably a slight advantage to the stimulation 
in that position. The alternation was made every 15 min. for 12 hours. 
Ten seedlings of Ltipinus albus , about 6 cm. long, in damp chambers 
showed six root-tips bent slightly in response to stimulation at 90°, one 
apparently in response to ioo°, and the other three roots straight. In 
a pot of twelve seedlings of Brassica alba , seven hypocotyls ben in 
response to the position at 90°, one apparently in response to ioo°, and 
the other four grew straight. In a pot of eleven seedlings of Raphanus 
sativus , seven hypocotyls bent in response to the position at 90°, and 
the other four grew straight. 
Alternation at 90° and 67-5°. — For this test seedlings of Ltipinus albus 
and of Helianthus annuus were used on the alternating rack. The former 
were in damp chambers, and were observed for the behaviour of roots ; the 
latter grew in pots of sawdust, and only their hypocotyls were studied. 
After the alternating process had been continued for eight hours at 
a temperature of 23 0 , all of the twelve Lupinus roots were curved in 
response to the position at 90° ; while of the fifteen hypocotyls of Helian- 
thus , twelve had bent in response to the position at 90°, and the other three 
remained straight. 
Alternation at go° and 45 0 . — Only one set of seedlings was tested 
at these angles — the primary roots of Lupinus albus. After the alternation 
had been continued for 5 hours in temperature 22*5°, eight of the twelve 
roots showed curves in response to the position of 90°; the other four 
roots remained straight. In this set of seedlings the hypocotyls were 
too short for good results and were not observed. 
The position at 90° stimulates to bending more strongly than at 45 0 , 
67-5°, ioo°, 112-5°, or I 35 °* From this we may infer that the position 
of strongest geotropic stimulation or response is 90° from the position of 
normal equilibrium. 
3. Determination of the angle for maximum response by the method oj 
the after-effect. 
Under the foregoing heading I have placed several experiments 
conducted after the manner of those of Czapek. Good seedlings were 
selected for the test, the glass tubes were shaped to fit the root-tips closely, 
and the revolution on the klinostat began immediately on the removal 
of the glass tubes. The tubes were washed thoroughly before using, were 
