The Mechanism of Curvature of Tendrils. 
BY 
D. T. MACDOUGAL, 
The State University of Minnesota. 
With Plate XIX. 
»♦ 
Historical and General Considerations. 
I N 1891 the writer began a series of experiments dealing 
with the features of growth and irrito-contractility of the 
tendrils of the Passifloreae. In 1892 a paper, concerning 
the principal features of the anatomy and morphology of the 
tendrils of Passijiora coenilea was published, and in the 
following year a second followed on the external phenomena 
of irritability and the coiling movements. In the course of 
the work many facts of significance in the determination of the 
mechanism of the movements, the localization of the motor 
zones, and the conduction of stimuli were brought to light. 
These facts, especially those concerning the first-named 
features, were much at variance with the generally accepted 
theories of tendril-curvature, and were not sufficiently verified 
by repeated observations at that time to justify their publica- 
tion with my other work. With the accession of later results 
by myself and others, the conclusions which follow seem 
entirely warranted. 
It may be useful in the following discussion to recall that 
complex organs of the higher plants which have the power of 
[Annals of Botany, Vol. X. No. XXXIX. September, 1896.] 
