CONDUCTING TISSUES 131 



In stems, this type of bundle may be completely 

 developed even in the primary stages of growth. 

 The open collateral bundle is the type most frequently 

 found in mature dicotyledonous roots and stems. 

 Bi-collateral fibro-vascular bundles consist of a xylem 

 element with associated cambium and two phloem 

 elements, one on each surface of the xylem. This 

 type of bundle is present in but few mature dicoty- 

 ledonous roots and stems. 



The various types of fibro-vascular bundles are 

 illustrated in Plates 47 and 48. The arrangement 

 of the different elements in each type of bundle is 

 represented in the diagrams accompanying these 

 illustrations. 



