Dec, 1906.] Silphium laciniatum. 39 



NODDING OF THE TERMINAL HEADS OF SILPHIUM LACIN- 

 IATUM. 



John H. Schaffner. 



During the past summer, while botanizing in Kansas, my 

 attention was attracted to a peculiar eastward tipping of the 

 terminal heads of Silphium laciniatum L. I had noticed such a 

 phenomenon before in the common sunflower, in which the ter- 

 minal heads, especially of small plants , normally tip to the north- 

 east. 



In the compass plant, anthesis begins in the terminal heads 

 and a strong eastward nodding was observed to be almost univer- 

 sal in these although the lateral heads appear to have the prop- 

 erty to only a slight extent. On July 7th and Sth, a large num- 

 ber of plants was observed in an open prairie lot near Ma3'etta. 

 The wind was from the east-southeast at the time and it is diffi- 

 ctdt to see how it could have had anything to do with the phe- 

 nomenon. Of 135 plants in bloom at the time, the terminal 

 heads of 123 faced in an easterly direction and 12 in other direc- 

 tions. But of these 12, several had imperfect peduncles. So 

 the percentage of indifferent normal heads was very small. 



The compass plant often grows in clusters of half a dozen or 

 more. Frequently the terminal heads of all the plants in a group 

 are in bloom at the same time and are tipping to the east. In 

 such cases the appearance becomes striking when contemplated 

 in connection with the north and south direction commonly 

 taken by the basal leaves. 



Later other observations were made at A^arious places as op- 

 portunity afforded and always a very large percentage of the 

 terminal heads were found nodding towards the east. 



In the common sunflower, the exposure of the large gi^een 

 involucre in the most favorable position with respect to the 

 rays of light must be a decided advantage to the plant. But in 

 Silphium laciniatum the involucre is rather insignificant and 

 appears to be of little importance as a photosynthetic organ. 



