198 BOTANICAL GAZETTE [MARCH 
The effect is most striking, however, in the case of plants with a 
single large head. It was observed that plants growing on the south 
2.—Cultivated H. annuus just Fic. 3.—The same plant as in fg. 2, 
Fic. s 
before sunset, showing westward nuta- at 7 A.M. the next morning, showing east- 
tion. ward notation. 
side of a house did not tip to the east but to the south. This may 
have been caused by the reflection of the sunlight from the. wall. The 
eastward position is often disturbed by the 
wind, so that the heads may appear to face 
in any direction. Sometimes the heads tip 
to the east while the stem below still con- 
tinues to nutate (figs. g, 5). This condition 
gave a very unique appearance to the plant 
when nutating in the evening. The same 
phenomenon has since been observed also in 
wild Helianthus annuus. After the seeds 
begin to develop the weight of the head 
bends the stem over, and the sharp angle 
caused by the tipping disappears (fg. °)- 
fig. 1, taken at six o’clock in the afternoon, 
: 6 shows well the mode of nutation and also t € 
grams showing 7 cieat eastward tipping of some of the flowering 
heads at anthesis (4,5), and heads. The tipping of the head is of advan- 
Position when fruiting (6). tage in bringing the bracts of the involucre 
