57 



Bundle. 



1. general ghaeacters. 

 Centric, i.e., the tissues are arranged in concen- 

 tric zones. 

 Closed, i.e., no generating tissue called cambium 



is present. 

 Cauline, i.e., each bundle is found to terminate 

 in the stem, and does not enter a leaf. 



2. TISSTJES. 



(a) Wood or Xylem, which shows two protoxylem 

 groups, and two sets of elements. These are 

 traclieides and parenchyma. Each tracheide 

 consists of an elongated, thick- walled empty 

 cell, whose great function is to carry water. 

 The traclieides are marked by bordered pits. 

 The parenchyma consists of smaller cells, re- 

 tains its contents, and stores up starch. 



(b) Bast or Phloem. This surrounds the wood, 

 and consists also of two sets of elements. 

 These are Sieve Tules (or Bast Vessels) and 

 'parenchyma. The Sieve Tubes are elongated, 

 contain protoplasm and various albuminoids, 

 but no nucleus. They are characterised by 

 perforations on their inclined and radial walls, 

 through which the contents stream. Their 

 great function is to conduct the albuminous 

 food material. The Parenchyma is thin- 

 wallod, each cell is nucleated and stores up 

 albuminous food material. 



