3 l6 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



the propagation of the contact disturbance. These structures have been called 

 contact papilla. Such papillae, of the external walls of the epidermis of a pump- 

 kin tendril, are shown in Fig. 157, B, where the shaded portion represents pro- 

 toplasm. A crystal of calcium oxalate is shown embedded in the protoplasm 

 of each papilla. 



Fig. 156. — Tendrils of Ampelopsis heterifolia. At the right a young tendril, with .swollen 

 tips; at the left, an old one with adhering disks, caused by contact with the wall, and coiled 

 basal part. {After Pringsheim.) 



§3. Circumnutation. 1 — Darwin showed that all growing plants, although 

 they seem to be elongating in a definite direction, are actually swinging about 

 in more or less circular paths, but that these movements are so slow or so slight 



A B 



Fig. 157. — A, Epidermal cells from tendril of Cucumis sativus, showing protoplasm- 

 filled pits in outer walls (contact papillae). (After Pfeffer.) B, Contact papillae of the outer 

 walls of tendril epidermis of Cucurbita pepo (pumpkin). (After Haberlandt.) 



that they are usually quite unnoticed, without the employment of special 

 methods of observation. Darwin thought that this sort of movement (which 

 he called circumnutation) is the fundamental, phylogenetically simple move- 



1 Darwin, Charles R., and Darwin, Francis, Power of movement in plants. London, 1880. Wiesner, 

 1881. [See note 2, p. 277.] 



