SUMMATION OF DISSIMILAR STIMULI APPLIED TO 

 LEAFLETS OF SENSITIVE BRIER (SCHRANKIA). 



By lewis B. bibb. 

 First Lieutenant, Medical Corps, U. S. Army. 



(Received for publication, January 15, 1921.) 



The writer has made experiments upon the leaflets of Schrankia 

 uncinata Willd, or sensitive brier (Fig. 1), to determine whether sub- 

 minimal stimuli of different character, such as chemical and mechan- 

 ical, when applied simultaneously would combine their effects so as 

 to reinforce each other and produce a visible response. Schrmtkia 

 appeared suitable for this purpose because the closure of one leaflet 

 mechanically stimulates the next distal leaflet and causes it to close 

 also (this will be referred to as secondary stimulus), and thus a wave 

 of closure is started which does not stop until all distal leaflets on the 

 same side of the mid-rib are closed. Moreover, the intensity of the 

 secondary stimuli is uniform as regards the leaflets of any given 

 pinna, but varies according to the time of day. The intensity of the 

 secondary stimulus is insufficient in the early morning to produce a 

 visible response, but in the late afternoon it is sufficient to provoke 

 prompt closure of the distal leaflets in turn. It was believed there- 

 fore that by choosing different times of the day for the experiment 

 the intensity of the mechanical stimulus due to the effect of one leaflet 

 on another could be varied at will, and that, at some optimum hour, 

 the stimulating effect referred to would barely fall short of provoking 

 a response. When this hour was found by actual trial in each indi- 

 vidual case, it was planned to apply subminimal stimulation and then 

 to observe whether the closure of one leaflet was followed by the 

 closure of the next distal leaflet; that is, in the early morning, a single 

 leaflet of Schrankia can be caused to close against the next distal 

 leaflet without causing the latter to close (Fig. 2). In the late after- 

 noon, on favorable days, the closure of any proximal leaflet inevitably 

 provokes closure of the next distal leaflet (Fig. 3). The problem was 



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