50 D. P. Pen hallow — Tendril Movements in 



one lies in the concavity of the upper surface, while the other 

 two occupy lateral positions, being situated at the extremities 

 of the major axis of the section. Within these areas (fig. 3 b, 

 b', b"), the tissue is found to be composed of rather large and 

 rounded, somewhat thin-walled, parenchyma cells (fig. 5) con- 

 taining protoplasm and a large amount of chlorophyll, while 

 there are also inter-cellular spaces and corresponding stomata 

 in the epidermis. Externally this tissue may' easily be seen 

 to extend the entire length of the tendril, forming three darker 

 green bands alternating with the more whitish green bands 

 of collenchyma tissue. The color distinction between them 

 is most obvious, both externally and in transverse section. 

 From the very prominent part which this tissue takes in the 

 ordinary circummutations of the tendril and the frequency 

 with which pointed reference must be made to it, we have 

 deemed a descriptive term essential. We have therefore 

 given it the name of vibrogen, or as signifying , that the 

 origin of the movement is to be found there. Immediately 

 within the collenchyma layer is a zone of rather large and 

 rounded parenchyma cells (c, fig. 3) consisting of three or four 

 rows, the innermost cells being smaller. This tissue connects 

 the three vibrogen bands through their inner portions. The 

 cells are filled with protoplasm, chlorophyll and other granular 

 matter, though the chlorophyll is conspicuously less than in 

 the three bands of vibrogen winch it unites with. It is 

 this layer of cells, however, which imparts the green color to 

 the tendril as a whole, modified as it is by the external layer of 

 collenchyma. Directty interior to this zone is a narrow belt, 

 within which the fundamental tissue becomes meristomatic at 

 a very early period, and ultimately — usually very early in the 

 growth of the tendril — gives rise to numerous rather small and 

 thin-walled wood cells (fig. 3 d, d', d"). In the earlier periods 

 of growth, this wood tissue will be found forming a crescent 

 alo*ng the lower side of the transverse section, as at c?, but later, 

 toward the left of the tendril, it arises opposite the two masses 

 of collenchjmia tissue near the upper side d', d", its interrup- 

 tion or want of continuity coinciding exactly with the want of 

 continuity in the collenchyma, or with the position of the 

 vibrogen tissues. Ultimately, however, these breaks may 

 close up, and the woody zone then becomes more or less con- 

 tinuous around the entire tendril. So long as the tendril arm 

 remains active, these wood cells are thin-walled (fig. 4 A), but 

 as age advances and activity diminishes, the wood cells are 

 found to become thicker and more resisting and finally assume 

 the appearance of all highly lignified cells (fig. 4 B), thus ulti- 

 mately defining the hard and woody nature so characteristic 

 of these tendrils after they have been for some time coiled 

 about a support. 



