LEWIS B. BIBB 525 



to ascertain whether subminimal chemical stimulation could be so 

 applied as to lower the threshold of susceptibility to stimulation and 

 cause the leaflets to behave in the forenoon as they normally behave 

 in the afternoon. 



Several attempts were made to transplant Schrankia, but such 

 treatment interfered with its reactivity. A spray of the plant was 

 isolated within an Erlenmeyer flask, with the object of securing a 

 definite concentration of chemical substance (chlorine gas or ammo- 

 nia fumes) in the atmosphere surrounding the leaflets; but this experi- 

 ment proved a failure because of condensation of water on the inner 

 surface of the flask. Attempts were made to summate subminimal 

 mechanical stimuli with subminimal stimulation due to the concen- 

 tration by a lens of the rays of the sun, and to summate mechanical 

 stimuli with stimulation of different acids, but these experiments failed. 



Finally, on June 22, 1919, at 11.15 a.m., the following experiment 

 was performed. Several pinnae of a plant growing in the open were 

 tested by touching a more or less proximal leaflet, and in each instance, 

 the touched leaflet closed without inducing closure of its next distal 

 neighbor. A petri dish containing ammonia water (27 per cent) 

 was then placed carefully underneath the adjacent compound leaf 

 (consisting of five pairs of pinnae) and after a few seconds, a single 

 leaflet of each of four pinnae was touched. In every instance, all 

 leaflets, on the same side of the mid-rib, lying distal to the touched 

 leaflet closed in a regular succession or wave. These results were 

 confirmed by repeating the experiment on June 24, at 4 p.m. 



On July 3, in the forenoon, several pinnae of an individual plant 

 were tested by touching one leaflet of each pinna. In every instance, 

 the touched leaflet closed without causing closure of the next leaflet. 

 A stream of chlorine gas mixed with air (10 per cent chlorine) was 

 then allowed to flow gently over each of several pinnae taken in turn. 

 6 seconds after the beginning of the application of the chlorine mix- 

 ture, a proximal leaflet was touched; it closed and caused the closure 

 of the next distal leaflet. The wave of closure proceeded until all 

 distal leaflets on the same side of the mid-rib were closed. The 

 fact that the leaflets on the opposite side of the mid-rib did not close 

 was accepted as proof that the chlorine mixture did not alone cause 

 the closure of the distal leaflets. All of several leaflets tested gave 

 similar results. 



