The Structure of Stems 



139 



Fig. 79. Photograph of part of a cross- 

 section of a bamboo stem, showing thick- 

 walled mechanical tissues massed in the 

 outer layers of the stem. The large open- 

 ings in each bundle are water-conducting 

 tubes. 



Fig. 80. Photograph of part of a cross-sec- 

 tion of a rattan stem, showing bundles. 

 The dark ring surrounding each bundle 

 is the mechanical tissue. The scattered 

 dark cells contain crystals of calcium 

 oxalate. 



dermis. The scattered arrangement of the bundles in the pith 

 may easily be seen in a stalk of corn. 



The monocot bundle. The monocot bundle differs from the 

 dicot bundle in that it lacks a cambium layer. It is frequently 

 called a closed bundle because, in the absence of cambium tissue, 

 the bundle cannot increase in size and there can be no growth in 

 diameter of the monocot stem through the multiplication of 

 cambium cells. The dicot bundle, on the other hand, is spoken 

 of as open, because there is a canibium layer between its water- 

 conducting and food-conducting tissues and the bundles can 

 increase in thickness. The monocot bundle differs further from 

 the dicot bundle in that its mechanical tissues form a complete 

 sheath about the food- and water-conducting parts. It is as 

 though the bast of the outer part of the dicot bundle and the wood 

 of the inner part were joined at the sides of the bundle, forming a 

 sheath about the conducting tissues. 



The fibers like sisal and Manila hemp (Figs. 81, 235) that are 



