324 



CONDUCTING SYSTEM 



fact are furnished by twining plants, and by climbers in general. In such 

 plants the construction of the conducting system is governed as 

 Westermaier and Ambronn have shown by two factors, namely the 

 great length of the conducting region and the relatively small cross- 

 sectional area available for the disposition of the conducting elements. 



Fig. 131. 



Diagram to show the leading anatomical differences between a tendril and a leafy 

 branch of the Vine. A. Sector of a T.S. through a fully-developed tendril. B. Similar 

 sector of a T.S. through a yearling branch ; I, leptome ; p, hadrome-vessels ; b, fibrous 

 strands. Primary hadrome and fibrous strands shaded. Both figures are drawn to 

 scale with the aid of a camera lucida. For further explanation see text. 



These conditions render it highly necessary that all features which 

 tend to lower the rate of conduction should be eliminated ; in the 

 case of water-conducting vessels the most serious obstacle to rapid flow 

 arises from the adhesion of the water to the walls of the tube. This 

 difficulty can be most readily overcome by an increase in the diameter 

 of the tube, since in the case of a cylinder of given height the area of the 



