1914] JOLIV ETTE—PILOBOLUS IIg 
In the experiment with the different incandescent filament 
lamps, as with the solutions and plates of colored glass used in the 
earlier work (1), Pilobolus fires its sporangia in larger numbers 
toward the lights in which the proportion of the blue rays is greatest. 
In other words, it is more responsive to actinic rays. The intensi- 
ties in the different wave-lengths, as earlier mentioned, are not 
measurable; but the uniformity of response in favor of the source 
containing the greater proportion of actinic rays suggests the 
superiority of the more refrangible rays over the less refrangible 
Tays in causing heliotropic curvatures. This question can be 
definitely settled only when the intensities of lights of different 
colors can be measured. 
The energy given off by the source of light apparently does not 
compare in effect with the distribution of the same in different por- 
tions of the spectrum. In the experiments using a 20-watt or 
16-candle-power tungsten lamp and a 32-candle-power carbon fila- 
ment lamp the large majority of the sporangia went to the tungsten, 
although its total energy was but half that of the carbon. From 
this it is apparent that differences in distribution in the spectrum 
outweigh in effect the differences in the total energy of the two 
sources. 
The set of experiments using a 16-candle-power tungsten against 
a tantalum of twice the number of candle-powers showed the dis- 
charge to be in favor of the tantalum. At first glance it appears 
that this contradicts the above results with the carbon and tungsten 
lamps, and suggests that the total energy of the source does play 
asi important réle in the results. However, on further considera- 
tion, it must be noted that the total number of actinic rays in a 
tantalum lamp of twice the intensity of the tungsten is probably 
Sreater than that in the tungsten. The solution of this point, of 
course, is bound up with the question of intensity and composition 
of the sources under discussion and cannot be taken with any 
degree of finality. With the tungsten lamp of approximately the 
same intensity as that of the tantalum, the discharge was in favor 
of the tungsten which emits a larger proportion of the blue rays. 
The difference as far as distribution in the different wave-lengths 
of the energy of the tantalum and tungsten lamps is not so great 
