116 BOTANICAL GAZETTE [FEBRUARY 
one opening is usually accompanied by a corresponding percentage 
on the other. It might be suggested that this may be due to the 
general condition of the culture at the time of the experiment. The 
accuracy might be affected by food supply, moisture, temperature, 
and other factors of importance to the physiological condition of 
the sporangiophores at the time of stimulation. 
Here, as in the previous experiments, the sporangia that strike 
outside of the opening are to be found for the most part in the first 
_ vertical strips to the left and right of the openings. An examination 
of the data (table VIII) will show a good proportion of the cases 
where all that were fired toward a single light are found on the 
opening or adjacent strips. Thus it is clear that the accuracy is 
much greater than it would appear from an examination of table IX 
alone. 
Summary 
Physiologists, in studying the reactions of plants to stimuli, 
have for the most part worked with phototactic organisms oF 
organisms of considerable complexity, individuals in which there 
was a differentiation of tissues, where the cells in one portion of 
the body may receive a stimulus, another perceive it, and still 
another respond to it. Such a study has the disadvantage of 
dealing with too many factors and accompanying phenomena. 
In Pilobolus the reaction is marked and can be easily studied. A 
single cell receives the stimulus and responds to it. The protoplasm 
of the cell receives the stimulus, perceives it, and reacts. The 
accuracy of response of Pilobolus toward the light is, remarkable, 
when we consider its size and the distance through which it throws 
its sporangia. The sporangiophore scarcely ever exceeds 1 cm. in 
length, and is usually somewhat shorter, while the distance through 
which it discharges the sporangium in most of the experiments is over 
25 times that measurement. The accuracy of response and the 
nicety of organization of such a mechanism can well be appreciated 
from the study of such experiments. From such work the capacities 
of a single cell can best be realized. 
The results of the experiments in which Pilobolus is stimulated 
simultaneously by two lights bear directly on Nott’s (4) theory 
