208 AVERRHOA. [CH. VIII 



drop, but by series of rapid rises and falls as represented 

 in fig. 41. In this diagram the numbers 0° to 60° on the 

 left represent the angular divergence in degrees of the 

 leaflet from the vertical, those on the right represent 

 temperature (C). Thus at 11-30 the leaflet made an 

 angle of 52° with the vertical, i.e. an angle of 38° below 

 the horizon while the temperature (the dotted line) was 

 31-4°C. The leaflet had been slowly rising for 25 minutes, 

 and at BR a blind was pulled up so that the plant was 

 brightly illuminated, when the leaf descended in 5 steps 

 to the paraheliotropic position, where it executed three 

 rapid movements (at about 80° below the horizon), until 

 at SH, when the blind was pulled down, it rose for 35 

 minutes, to be again disturbed by sunshine at br'. In 

 performing this experiment the windows must be opened 

 when the blinds are pulled up, to equalise the temperature 

 as much as possible. 



The obsei"vations here recorded were made as follows. 

 The main petiole of the leaf to be observed pointed straight 

 at the observer, being separated from him by a vertical pane 

 of glass. The petiole was fixed so that the pulvinus of 

 one of the lateral leaflets was at the centre of a graduated 

 arc placed close behind the leaflet. A fine glass filament, 

 attached to the leaflet and projecting like a continuation 

 of the midrib, served as an index. As the leaflet rose and 

 fell its angular movement was recorded, by reading at 

 short intervals of time the position of the index on the 

 arc. To avoid errors of parallax the readings were taken 

 by looking through a small ring painted on the vertical 

 glass in a line with the pulvinus and the centre of the arc. 



