118 BOTANICAL GAZETTE [FEBRUARY 
affect the reaction to the other. To this degree the results are 
corroborative of Noti’s theory. But Notw’s theory, based on his 
work with light and gravity as stimuli, suggests a change of geoto- 
nus due to the presence of the light. In working with the two light 
stimuli, the reaction to one of the two stimuli to the exclusion of 
the other cannot be explained in this way, although here, as above, 
the plant is subjected to two directive influences. 
Where the two simultaneous stimuli were of different kinds, 
gravity and light, Nott believed that light may call forth certain 
changes in the plasma which, directly or indirectly, cause the reac- 
tion. He says that perception and reaction may rest on entirely 
_ different characters; but the reaction may be carried out by the 
same changes. In work where the two simultaneous stimuli are 
of the same character, as in the present experiments, the reaction 
is less complicated. Thus but two sets of changes of the plasma 
need be concerned with the response. 
The above experiments show that there is no sign of a resultant 
reaction, but that they can in no way determine whether, so far as 
perception is concerned, there is any influence of one light on the 
other. According to Noxt’s theory, a change of geotonus takes 
place, due to stimulation by light; that is, there is a change of 
sensibility to gravity as such due to the perception of light. The 
question arises whether, with the presence of two light stimuli of the 
same kind acting through the same time, there is a corresponding 
change of sensibility toward one light owing to the mere presence of 
a second of a similar kind. Apparently there must be some factor 
or factors somewhere in the organization of the plasma that brings 
about a total neglect of one stimulus and a complete reaction toward 
another of a similar nature, since the reaction is not a resultant one. 
It appears that Nott’s theory alone is insufficient to explain entirely 
the lack of resultant reaction to two directive forces when applied 
to an organism as contrasted with the results obtained by physicists 
in working with inanimate matter. The question, then, of what 
determines the reaction toward one light and a lack of response 
toward the second is still unsettled, and the explanation must be 
deferred to a time when more is known of the intricate mechanism 
and ultimate organization of the plasma of the cell. 
