On the Movements of Petals 13 



The foregoing summary of the work done on this problem 

 since 1686 shows how very varied have been the theories as to 

 the cause of the movement of floral leaves, and the great need 

 for further investigation. Many of the articles which support 

 good theories show evidence of a small or inexact amount of 

 experimentation. This, I have tried to avoid by endeavoring to 

 prove all statements by actual experiment, so that the final result 

 should be conclusive. As to the exact processes which are car- 

 ried on within the flower, or plant, to bring about movement, 

 there is yet much to be done. 



EXPERIMEMTAL METHODS. 



Information as to the cause of floral movements was sought 

 in two ways : first by means of field observations, and second by 

 means of experiments performed either in the field or greenhouse, 

 mostly the latter because of the greater ease with which the sur- 

 rounding conditions could be controlled. The aim was to elim- 

 inate the possible physical factors, such as light, humidity, etc., 

 one after the other. For example, in order to prove that humid- 

 ity could not cause the opening of the flowers of the morning 

 glory, light, heat, and the water-content of the soil were made 

 the same in three instances : in one of these the air was made 

 very dry, in another very moist, and in the third it was kept nor- 

 mal. The procedure was the same for the elimination of the other 

 factors. The apparatus used for these experiments was very 

 simple. For example, in the humidity experiment cited above, 

 two large bell jars, thermometers, a psychrometer, calcium chlo- 

 ride for absorbing moisture, and a piece of sheet rubber to tie 

 around one flower pot were used. Water-content and light re- 

 quire tin cans for soil samples, thermometers, photometers, and 

 a shade tent. To ascertain whether heat influences opening and 

 closing of flowers, several simple pieces of apparatus were neces- 

 sary. A tin box, 2x2x2 ft., collapsible like the small tin 

 dinner boxes, was constructed to be used in field work, but was 

 also found useful in indoor experiments. The top and one side 

 were made of glass ; a hole }i of an inch in diameter was cut in 



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