Parr. — 
The Response of Pilobolus to 
Light . 
19 : 
Light 
Series 
Wave¬ 
Temp. 
Time of exposure 
% Posi¬ 
% Indif¬ 
Presentation 
source. 
No. 
L OlOUr • 
length. 
°C. 
in min. 
tive. ■ 
ferent. 
time in min. 
Tungsten 
Bt 9 
Blue 
±470 
24 *7 
5.37-6.30 = 53 
20 
80 
lamp 
Bt 10 
11 
11 
23-6 
4.46-5.41$ = 55$ 
94 
6 
Bt 11 
11 
11 
23-5 
7.00-7.54 = 54 
37 
63 
55 
It 6 
Indigo 
±464 
24-3 
5.45-6 43 = 58 
66 
33 
It 7 
11 
24-8 
4 - 3 S- 5-33 = 55 
60 
40 
It 8 
>> 
11 
25-2 
6 - 45 - 7*35 = 50 
25 
75 
55 
las 
5> 
±437 
24-9 
6.34-7.24 = 50 
0 
100 
la 9 
>> 
11 
25-2 
7.09-8.03 = 54 
32 
68 
la 10 
)> 
11 
24*0 
4.45-5.42 = 57 
84 
16 
54 
Va 1 
Violet 
± 4 r 4 
25-2 
5.00-5.53 = 53 
92 
8 
Va 5 
11 
11 
25*1 
5.21-6.12 = 51 
50 
50 
Va6 
11 
25-3 
6.12-7.02 = 50 
0 
100 
5 i 
Vt 12 
11 
± 39 8 
25-2 
3.59-4.58 = 59 
100 
0 
Vt 13 
11 
11 
23*5 
5.05-5.52 = 52 
25 
75 
Vt 14 
11 
11 
23-8 
5 - 37 - 6.2 r = 50 
33 
66 
50 
In Fig. 2 the spectral energy curves for the Nernst and for the tungsten 
lights represent in graphic form the data recorded in Tables II, IV, and V. 
Wave-frequencies of light are represented by the ordinates and the 
mechanical energy in ergs per second by the abscissae. A comparison of the 
above curves with those of Coblentz (1911) for the Nernst and the tungsten 
lights, and those of Moll (1907) for the Nernst light, will show that a higher 
value was obtained in the violet. Although repeated attempts were made 
to bring these results in the violet into conformity with those of Coblentz 
and Moll, they were not successful. The difference may be in part due to 
the use of the Nernst lamp with the globe removed. 
A number of investigators have maintained that the response of 
organisms to light of different nature may be correlated with energy 
equivalence. Pilobolus , exposed to the spectral regions of the Nernst and 
tungsten lamps differing rather widely in energy, will respond as indicated 
in Fig. 3. In plotting these graphs the wave-lengths and frequencies are 
disregarded. The abscissae * represent the presentation time and the 
ordinates the energy of the region expressed in ergs, the data being taken 
from Tables IV, V, VI, and VII. 
An inspection of Fig. 3 shows that an actual decrease in the rate of 
response takes place with increase of the photic energy. This shows, con¬ 
clusively, there is no direct relation between response and the energy of the 
different regions. Thus, the lens theory of Haberlandt (1905) and the 
orientation theory of Radi (1903), that response is due to a pressure that 
the light exerts on the cells of the organ, are not applicable to the response 
of Pilobolus . 
Likewise, a statement in Blaauw’s theory of response (1909, p. 30), 
namely, that the plant perceives only the quantity of energy as a stimulus, 
cannot be taken literally, for he says: ‘ Fur diesen konstanten Efifekt ist 
eine konstante Quantitat Energie notig und es ist also fur die Pflanze 
gleichgiiltig, wie diese Energie, fiber Zeit und Intensitat verteilt, zugefiihrt 
wird. Die Pflanze empflndet nur die Quantitat Energie als Reiz ; die 
O 
