FIBRO- VASCULAR BUNDLES. 



14:? 



Fig. 57.~ Cross section of Concentric J/undle of 

 Rhizome of Iris with central sieve portion sur- 

 rounded by vessel portion. (Tschircn). 



Types of the Fibro Vascular Bundle. 



The individual tissues which collective- 

 ly form a Fibro-vascular Imndlo may be 

 grouped in vnrious combinations. An- 

 atomists describe three principal typos 

 based upon the relationship that the ves- 

 sel portion, or Xylem (in the wider 

 sense), bears to the Sieve portion or 

 Phloem (in wider sense). These are 



1. Radial. 



2. Concentric. 



3. Collateral, of which three forms 

 are described. 



1. The Radial Bundle is uue in which 

 the xylem and the phloem lie side by 

 side, alternating with each other radial- 

 ly. The xylem starts at the center and 

 builds strong ribs of tissue between which 

 lie the phloem ehMuents. Radial bundles 

 are characteristic of young roots, and ac- 



vie- -W -Cross section of developinff open Collateral bundle, g. vessels. ^ tracheids. with hbnform 

 betifeencSiSthrsylempartofthebu^ r. cambium between it and y. sieve tubes b 



bast lb?es wit h ^ ^^^ P^^^^"" ^^'^ ""^ 



the bundle. (Sachs). 



