In bright sunshine the leaflets assume a highly inclined dependent position.  A leaflet in diffused light was observed rising for 25 m.  A blind was then pulled up so that the plant was brightly illuminated (BR in Fig. 134), and within a minute it began to fall, and ultimately fell 47o, as shown in the diagram.  This descent was performed by six descending steps, precisely similar to those by which the nocturnal fall is effected.  The plant was then again shaded (SH), and a long slow rise occurred until another series of falls commenced at BR’, when the sun was again admitted.  In this experiment cool air was allowed to enter by the windows being opened at the same time that the blinds were pulled up, so that in spite of the sun shining on the plant the temperature was not raised.

The effect of an increase of temperature in diffused light is

* In all the diagrams 1 mm. in the horizontal direction represents one minute of time.  Each mm. in the vertical direction represents one degree of angular movement.  In Figs. 133 and 134 the temperature is represented (along the ordinates) in the scale of 1 mm. to each 0.1 degree C. In Fig. 135 each mm. equals 0.2o F. [page 333]

shown in Fig. 135.  The temperature began to rise at 11.35 A.M. (in consequence of the fire being lighted), but by 12.42 a marked fall had occurred.  It may be seen in the diagram that when the temperature was highest there were rapid oscillations

Fig. 134.  Averrhoa bilimbi:  angular movements of leaflet during a change from bright illumination to shade; temperature (broken line) remaining nearly the same.

of small amplitude, the mean position of the leaflet being at the time nearer the vertical.  When the temperature began to fall, the oscillations became slower and larger, and the mean position of the leaf again approached the horizontal.  The rate of oscillation was sometimes quicker than is represented in the above diagram.  Thus, when the temperature was between 31o and [page 334]

Fig. 135.  Averrhoa bilimbi:  angular movement of leaflet during a change of temperature; light remaining the same.  The broken line shows the change of temperature. [page 335]

32o C., 14 oscillations of a few degrees occurred in 19 m.  On the other hand, an oscillation may be much slower; thus a leaflet was observed (temperature 25o C.) to rise during 40 m. before it fell and completed its oscillation.

Fig. 136.  Porlieria hygrometrica:  circumnutation and nyctitropic movements of petiole of leaf, traced from 9.35 A.M.  July 7th to about midnight on the 8th.  Apex of leaf 7 ½ inches from the vertical glass.  Temp. 19 1/2o — 20 1/2o C.