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364 



BOTANICAL GAZETTE 



[may 



nutation, nor am I aware that any other plant has been observed to 

 share with Helianthus the distinction of being a ^' sunflower." 



During the past four or five years my attention has been repeatedly 

 attracted to other genera that exhibited a diurnal motion almost iden- 

 tical in kind with that of Helianthus, and almost if not quite as marked. 

 The accompanying illustrations of Bidens frondosa show the extent of 



Fig. 2.— Group of Bidens frondosa, i^V^xv in the morning, to show prevailing 

 eastward nutation (to the left), 



the nutation in this species. Fig, i shows one plant in the morning at 

 10 o'clock. The exposure occupied about one minute and it is evident 

 that the curvature is not due to the wind, nor had the wind been blow- 

 ing. I have repeatedly observed this same plant in the afternoon and 

 found the westward nutation fully as marked as is the eastward in this 

 illustration. Fig. 2 shows a mass of plants of the same species in the 

 morning, and illustrates the extent to which this habit preponderates 

 among individuals. Thesame group taken at four o'clock the same after- 

 noon is shown m fig. 3, This is simply a small portion of a roadside 

 patch of weeds that extended for miles. Several counts showed that 



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