108 BOTANICAL GAZETTE [FEBRUARY 
radiant energy. The following experiments, therefore, are qualita- 
tive only; but I hope they will prove suggestive. 
The different colors of the spectrum are represented in different 
proportions in the various incandescent lamps. These filaments 
are of standard make and the energy of the bulbs is measured in 
candle-powers. Thus by using bulbs of equal candle-power and 
current of known intensity we shall have somewhat comparable 
quantities. 
Although this method is not all that could be desired, it has a 
very marked advantage over the colored solutions used by SACHS, 
and also the monochromatic glass plates that are so generally used 
in work on the effects of rays of various wave-lengths. The colored 
solutions absorb a large portion of the total energy emanating 
from the source, different solutions differing in this respect. In the 
case of the solutions (and it is also true of the colored plates) : 
neither the intensity nor the energy of the lights can be compared. 
The incandescent lamps offer at least the advantage that they are 
of nominal commercial value; and with the advent of the knowl- 
edge of methods of comparison of intensities of colored lights, some 
exact idea of the intensities in the different parts of their spectrum 
may be obtained. Some study has been made to determine the 
distribution of the different wave-lengths in the different incandes- 
cent lamps, but so far it is insufficient for the present instance. It 
is known, however, that of the three incandescent lamps used in the 
experiments, the tungsten has the largest proportion of the actinic 
rays, the tantalum next, and the carbon least. The results with 
these filaments may thus serve to check up with those of the earlier 
work, in which the solutions and the plates of colored glass were 
used. 
Experiments were made in order to test the relative efficiencies 
of different incandescent lamps in bringing about the reaction of 
Pilobolus. In these experiments the carbon filament, the tantalum, 
and the tungsten were compared. The experiments were per- 
formed in the dark room, using the redwood light-proof box already 
described. The openings were 1 cm. in diameter and the distance 
between them from center to center was 1o cm. The culture was 
placed 23 cm. from the point midway between the two openings. 
