Macfarlane, The Sensitive Movement» of some Flowering Plauts. 179 



extremity. Under a green screen tlie time movement practically 

 coincides with that of exposed plants, and is beautifully regulär 

 in sequence. According to the climatic environment for each day, 

 variations in the time movement of the species are shown. This 

 is seen from the record of Oct. 3rd for Oxalis stricta. These 

 variations are probably due to moisture, illumination und tem- 

 perature efFeets either separately or combined. 



Under the blue light there is always a distinct retardation of 

 the normal nyctitropic period to the extent of from V2 to 2 1 /g 

 hours, the variations seeming to depend on temperature, on length 

 of exposure to the blue light, and on relative inten sity of the light 

 for the day. 



The relative period of unfolding in the morning has not beeil 

 determined with sufficient accuracy as yet, but likewise varies 

 under the different screens. If the peculiar results that were got 

 on September 17 th when the plants were uncovered, prove to be 

 trustworthy and general, they indicate a remarkable reversal of the 

 behavior exhibited when the plants were first covered, and an 

 equally remarkable reversal of the nyctitropic relations that ob- 

 tained while the plants were covered. 



These observations seem further to Warrant us in concluding 

 that up to 38 ° C, or even 43 ° C in some species, heat rays either 

 fail to stimulate the tissues, or if they do that their actions is 

 interrupted or antagonized by some other form of energy, though 

 this is scarcely likely. The same is true of the less retrangible 

 light rays, and of these the orange-yellow, yellow and yellow- green 

 seem to give the most uniform results, for so long as plants were 

 exposed to intense light the leaflets remained either quite flat or 

 became slightly reflexed. Under the green screen the leaflets of 

 C. nictitans and C. chamaecrista, when strongly illuminated remai- 

 ned flat or became inflexed in some cases to 25 °, but those of C. 

 Tora under equal illumination inflexed through an angle of 15°; those 

 of Oxalis stricta remained flat. The paraheliotropic movement thus 

 started under the green screen in some species became greatly 

 more pronounced under the blue in all, and during intense illu- 

 mination in Oxalis almost amounted to the nyctitropic position. 



Grouping the above facts, the conclusion is reached that the 

 heat rays, the less refrangible rays, and the more refrangible rays 

 are all trophic up to a certain point. When that point is crossed 

 the heat rays and less refrangible rays continue to be trophic up 

 to a much higher point, but the more refrangible rays (from green - 

 blue to violet) act as a stimulant or irritant. 



Oltmanns*) concludes from his experiments with white light 

 that Darwin's division of leaf positions into diaheliotropic and para- 

 heliotropic is superfluous, since he considers that the transition from 

 the one to the other is gradual and is determined by relative 



i: ) Flora, 1892, p. 251. 



12* 



