67 



gap the bundles which enter the leaves arise. 

 These are called common bundles. In the 

 petioles (leaf stalks) the bundles run straight. 



ii. Structure. The bundles are 



Cauline, i.e.^ they do not enter the leaves. 

 Centric^ i.e., the tissues form concentric zones. 

 Closed, i.e., there is no generating tissue 

 caDed Cambium present. 



Each bundle is surrounded by a continuous sheath 

 di:fferentiated from the ground tissue called the 

 Endodermis. This is only one cell thick ; the 

 cells are cuticularised on their radial walls, and 

 store up starch. 



Next to the Endodermis is found the Pericycle, 

 which is usually many cells in thickness. It 

 also serves to store up starch. In Phanerogams 

 the Pericvcle is seldom more than one cell thick. 



Within the Pericycle is found the Phloem (Bast). 

 The Phloem lying next to the Pericycle is called 

 Protophloem, and consists of small parenchy- 

 matous cells. Eying within the Protophloem is 

 found the Metaphloem, which consists of paren - 

 chyma and sieve-tubes ; these last, as their name 

 implies, are tube-like structures : the perfora- 

 tions or pores which characterise these elements 

 are found on their radial walls. The companion 

 cells of the angiosperms are not found here. The 

 function of the Phloem Parenchyma is to store 



