120 BOTANICAL GAZETTE [FEBRUARY 
as is the case of that in the carbon and tungsten lamps. This may 
account for some of the differences in the distribution of the spo- 
rangia in the two cases, when comparing the tungsten with the 
carbon and with the tantalum. 
A comparison of the carbon and tantalum lamps shows again a 
majority of sporangia discharged on the opening before the tantalum 
lamp which contained the larger proportion of blue rays. 
In the experiments with the rays of different wave-lengths, 
although the stimuli are both light stimuli, there is a marked dif- 
ference in composition. We have then an extra factor to deal 
with; but, as in the experiments with the two nearly equal light 
sources, there is no sign of a resultant reaction. There is no sign 
of a change of aim toward one light owing to the presence of a 
second light. With the tendency of the sporangiophores to dis- 
charge toward the blue light, however, it is plain that there is no 
uniform aim of all the sporangia subjected to the two lights to go 
to the light having the larger proportion of the blue rays. Why 
does not Pilobolus always discharge toward the source of light hav- 
ing more of the actinic rays? The difference in the length ot the 
light ray does bring a marked variation as regards the numbers fired 
toward the two sources. Still, some are fired toward the less favor- 
able of the two sources. 
The accuracy of aim toward the two lights might well be’ said 
to agree in general with that already found for the two light sources 
used in the above experiments. However, there is a noticeable 
difference in accuracy of aim toward the different filaments, and 
that for the most part is in favor of the light with the larger pro- 
portion of the more refrangible rays. With the solutions and 
glass plates used in the earlier work (1) there was a much greater 
difference noted. There is a probability that the smaller difference 
may be due to less difference in light intensity, to a smaller differ- 
ence in composition, and also that there is a limit to the accuracy 
of response toward any source of stimulation, and that in aiming 
at the lights in use in these experiments they reached that limit, 
the less effective lamp being sufficient, or in some cases nearly 
so, to bring about as accurate a reaction as is possible to the 
plant. 
