402 BOTANICAL GAZETTE [JUNE 
From the above it is demonstrated that the irritability which is 
responsible for the bending of the stem is not inherent in the 
stem -itself, but the stimulus is received by the lamina of the 
leaf, and the impulse transmitted through the petiole to the stem 
produces a response from both these parts. 
NUTATION OF THE HEADS BEFORE ANTHESIS. 
About July 15 the behavior of the young heads began to be 
observed. It was found that both the terminal heads and those 
on side branches nutated to the same extent as the leaf buds. 
Young heads on long, naked stems coming from the axils of 
leaves nutated also, the bracts of the involucre acting no doubt 
the same as the ordinary leaves. When the leaves were removed 
from the stems bearing heads, the nutation did not cease. Thus, 
on August 2 the leaves were removed from plants having young 
heads, and the next day these nutated 50° east in the morning, 
and go° west in the evening. This experiment was repeated 
many times with both terminal and lateral heads, always with 
the same results. After the leaves have been removed from a 
plant having forty or fifty heads the effect of the nutation 
becomes quite striking. 
THE DISK DURING ANTHESIS. 
The nutation of the heads continues until anthesis begins. 
At this time the stem below the head hardens, which makes 
further nutation impossible. During anthesis the head is tipped 
sidewise until it stands with its face almost vertical, and this 
nodding is nearly always toward the northeast, although it 
may be east or north also. During favorable weather, at least 
90 per cent. of the open disks will be found facing the northeast, 
both in the morning and in the evening. The heads are not dis- 
turbed by light wind, but a strong wind twists the stems and 
thus greatly disturbs the normal position of the heads. Whole 
acres of plants were observed in regard to these points. ne 
eastward position of the disks readily deceives one into thinking 
that the face moves with the sun, especially when observations 
