82 THE AMERICAN NATURALIST. (Vor. XXXIX. 
experiments the plants were allowed to stand upright for half an 
hour after the last exposure, before making the final observation. 
In no case did this modify results in favor of the deviation of 
135 degrees, while with few exceptions, the plants, after this 
treatment, showed more pronounced curves in favor of the devi- 
ation of 9o degrees than they did at the close of stimulation. 
This was true whether alternation was begun from the position 
of 90 degrees deviation or from that'of 135 degrees. 
Marked differences in sensitiveness, indicated by the length of 
time required to produce curvature, were shown not only by 
plants of widely different genera but by different individuals of 
the same species and by the same individual at different times. 
Of the 395 plants used in these experiments, 53 did not 
respond in the time given to the experiment, and are simply to 
be considered less sensitive than their fellows showing curva- 
ture. Of the 342 that did curve, 331 or 96.8 % responded bet- 
ter for the deviation of 90 degrees, 11 or 3.2 % only, for the 
deviation of 135 degrees. 
Table I. Results Obtained by Alternating Stimulation. 



Time | No Curvature at Deviation of 
No. Material. Temp. | Hrs. Min. | vature. 9o degrees 135 degrees 
Young plants. 
6 | Chrysanthemum 2— o 3 3 9 
6 " 139 C | 3— 20 2 4 o 
5 " 189 C | 3— 20 I 4 2 slight o 
5 " 219 C | 3 — 40 o 5 o 
6 * 23°C| 3— o o 6  rslight o 
10 X 22°C | 7—45 o 10 o 
9 | Ageratum 20°C} s— o| o B o 
5 | Heliotropium 222C| 4— o o 5 2veryslight | o 
7 | Lavandula 239 C | 3 — 40 o 7 slight o 
7 " :222C| 3— o o 7 o 
3 " 222C| 2—40|. o 3. slight |o 
10 | Fuchsia 25°C] 2— o o 10 o 
10 “u 18°C} 2—40| 5!| 5 ud 
9 " 20 C | 3 — 40 o 9 o 
9 | Coleus 239C| 3— o o 7 2 very slight 
2 " 229C] 240] o o 2 very slight 
Seedlings. 
8 | Linum 1 o 
150 | Raphanus sativus | 24°C} 2— o 3 1248 2 








"After standing upright 30 minutes, all were curved in favor of go degrees 
deviation. 
