Macfarlane, The Sensitive Movements of some Floweriug Planta. 137 



C. nictitans and C. chamaecrista grow abundantly together in 

 tlie sandy soil of New Jersey, and are greatly modified in growth 

 according to environmental relations. If tlie seeds of the fornier 

 gerniinate under the shade of shriibs or trees, there is forined a 

 simple upright axis, or one bearing two to four short basal side 

 branches. But if shade d for sorae hours and exposed to the hot 

 sun for some hours the main axis remains relatively short, while 

 morenumerous and vigorousshoots than in the firstare formed. If fully 

 exposed to sunlight in a dry, sandy soil, the main axis remains 

 short and bears numerous side branches which again branch, so 

 that the entire plant assumes a dense, spreading, caespitose habit. 

 Every transition type ean be gathered between those now described, 

 each indicating in habit a distinct relation to its environment. 



Comparison of a lot of these plants that have grown under 

 varying conditions of moisture and illumination, yield instructive 

 results. During the hot season of July, August and the earl) r part 

 of September, when the thermometer registers 29 — 36° C during 

 day, and rarely falls below 19 — 24° C at night, the leaflets recover 

 from their nyctitropic State about 5 a.m. From then tili 7 or 

 7 : 30 A.M. the leaflets are quite Hat as a rule in all. But there- 

 after differences appear. If the morning is rather hazy, or if the 

 plants grow for the time under shade, the leaflets remain Hat tili 

 10 — 10:30 a.m., even though the temperature has risen to 27° C. 

 But if the morning sunlight be not obscured the leaflets of exposed 

 plants will curve forward and upward in paraheliotropic movement, 

 so that by 7:30 — 8 they will have moved through an angle of 

 18—20°, the thermometer it may, be mean while registering only 

 24 — 25° C. If, again, the plants are shaded by oak or other trees 

 the temperature may rise during day to 37 — 38° C, and yet the 

 leaflets will remain flat or nearly so. As a rule, however, it may 

 be said that direct insolation, or reflection of light from a white 

 surface when the temperature is 28° C, causes the leaflets to move 

 within two minutes in C. nictitans and C. chamaecrista. 



The above, and numerous similar observations led nie to 

 suspect that certain of the light rays, and not the heat rays, were 

 the exciting agents. To verify this if possible, a series of colored 

 glass screens were arranged so as to exclude all rays except those that 

 each color of glass allowed to pass. Mr. Arthur T. Collins 

 carelully tested the glasses with me by aid of his spectroscope, 

 and the results are subjoined. One that to the eye appeared a 

 rieh violet proved, when tested, to be a dull glass that allowed 

 only the less refrangible red rays and the violet rays to pass, and 

 that absorbed the remaining rays of the spectrum. The results 

 obtained with it are peculiar, but these will not be recorded in 

 this paper. As the blue glass passed:- orange the violet rays, a 

 fair index is got of the action of these on plants. 



Red glass : — red and orange rays unobstrueted, yellow almost 

 cut out, green, blue and violet cut out. 



