TWINERS AND OTHER CLIMBING PLANTS 



279 



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

 of each papilla. 



§3. Circunmutation.' — 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 sUght 

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

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



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.) 



A B 



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

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

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



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

 ment from which other plant movements due to unequal growth have evolved. 

 Wiesner has maintained, however, that this hypothesis is not tenable; in many 

 growing organs, he failed to find any circumnutation. Where it occurs it is 

 caused merely by inequalities in the rate of elongation on diSerent sides of the 

 axis. 



' Darwin, Charles R., and Darwin, Francis, Power o£ movement in plants. London, 1880. Wiesner, 

 1881. [See note 2, p. 24S.J 



