﻿the Physiology of Tendrils 67 



of the cross section would expend one-sixth of its length in pass- 

 ing the medulla and xylem, two sixths in passing through the 

 phloem and three sixths in the cortex and epidermis. The struc- 

 ture allows great flexibility, rapidity of reaction, and admits of 

 curvature in any direction. A further adaptation to these demands 

 consists in the extremely small size of the cells. 



The epidermal cells are rich in protoplasm, the outer walls are 

 markedly outwardly convex, and the three diameters of the cell 

 are nearly equal. The cortical cells impinge directly on the epi- 

 dermis, and a most notable fact is the entire absence of an extcr- 

 nal layer of collenchyma. The cortex contains a large amount 

 of chlorophyl and the globoid cells are arranged in six to eight 

 layers with marked intercellular spaces. The inner boundary of 

 the cortex is marked by a sheath consisting of one to three layers 

 of cylindrical parenchymatous cells completely filled with a densely 

 granular substance resembling the gluclosides. Similar cells oc- 

 cur in the phloem and even in the xylem. The medulla is com- 

 posed of very small elongated cells which have become sclerosed. 

 The tendril then consists mechanically of a cylindrical core of 

 mechanical elements enclosed in a thick cylinder of motor tissue, 

 both of which have a strictly radial symmetry. 



Irritability. 



The tendrils appear equally sensitive over their entire length 

 and at a temperature of 33 ° C. react to contact after a latent period 



~r - , 1 ■ t u ~..:~:^1 «nci'h'nn in 10-12 minutes 



of 5-10 seconds and regain the original position in ro-12 minutes 



if the contact is but momentary, tf a tendril is P reSSed by memS 

 of tweezers or the thumb and finger, no curvature is induced, since 

 the organ is equally stimulated to curve in opposite directions 



When plants growing in the open air are examined, it is diffi- 

 cult to find them in a « normal" or unirntated condition, sine they 

 are in a state of rapid circumnutation, are very flexible and easily 

 swayed by the wind ; then the contiguity of the two tendrils m a 

 pair allows them to be thrown together very easily. As a r< ult 

 of these facts, the tendrils are generally more or less curved into a 

 Wi, r :„ ...u:„u Ai*i™ th«v will more readily grasp a twig 



