140 



KANSAS Academy of science. 



OBSERVATIONS ON THE NUTATION OF SUNFLOWERS. 



BY W. A. KEIiLEBMAN, PH.D., AGE. COLLEGE, MANHATTAN, KAS. 



It is a common and apparently almost universal belief, that the sunflowers turn 

 ■with the sun; that is to say, that the disk is turned in the morning toward the east, 

 and that it slowly moves southward until noon, and then westward till night, keep- 

 ing pace with the apparent motion of the sun. This belief in case of most people 

 rests, so far as I can determine by inquiry, not so much on direct observation as on 

 hints and assertions of others. It is, in fact, mainly traditional. 



That there is some movement, has undoubtedly been observed by very many, 

 but how general and extensive in scope it is, is less accurately known. To determine 

 this point for my own satisfaction, I undertook the past season to make a careful 

 record of observations on the commonest of our native sunflowers, namely, Heli- 

 anthus annuus, which is considered to be identical with the commonly-cultivated 

 species. These observations are recorded in tabular form below. 



The record, commenced September 2, was interrupted September 4, 5, and 6. It 

 was resumed September 7, and continued until September 17. 



The observations were made usually between seven and eight o'clock in the morn- 

 ing, and between live and six in the evening. When the wind was very strong, so 

 as to interfere with the normal position of the heads, no observations were recorded. 

 Following the tabulation will be found a record of the daily direction of the wind. 



The plants observed, forty in number, were for the most part in a small, nearly 

 level pasture field. A few of them were near trees, but the position of each plant is 

 stated in the tabulation below. Some of them had but a single head, the majority 

 had several, and one plant had thirty-five heads. They were of various heights, 

 ranging from sixteen inches to eleven feet. 



No compass was used in determining directions, but as th^ fences around the 

 field were exactly east and west and north and south, it is not presumed that many 

 grave errors were made. The directions noted were north, south, east, west, north- 

 east, southeast, northwest, southwest, north-northeast, east-northeast, east-southeast, 

 south-southeast, north-northwest, west-northwest, south-southwest, west-southwest, 

 and all of the points between those already named (as north by east, north by north- 

 east, etc.), making thirty-two in all, or twelve and one-half degrees between each. 

 It is then plain that the slightest movement detectable without an instrument could 

 be recorded. 



Before proceeding to an analysis of the table, it might be stated that observa- 

 tions were made Sept. i), on Helianthus rigidus. About 110 heads of exposed plants 

 occupying a very small area by the roadside were counted at 9 a. m. It was found 

 that nearly all of them were turned southeast upward; a few were directed eastward, 

 and a few southward. At 6 p. m. they were again carefully observed, when it was 

 found that most of the heads had turned slightly more southward. 



A similar count was made of blooming heads of Helianthus anmius near the 

 preceding cluster on the same day (Sept. 9). Four hundred and twenty heads were 

 counted in the morning, and five hundred in the evening. No note was taken of 

 directions between the cardinal points of the compass; those heads were therefore 

 omitted that were exactly between these points, but all others were included. The 

 result of these two counts is as follows: 



MOKNING. 



Heads turned 

 toward the 



East 158, or 37.62% 



South 133, or 31.66% 



West 58, or 13.80% 



North 71, or 16.90% 



Heads turned 

 toward the 



East 179, or 35.80% 



South 168, or 33.60% 



West 104, or 20.80% 



North 54, or 10.80% 



