STEM STRUCTURE 169 



substances, the most important from the histological 

 standpoint are chlorophyll grains, starch, calcium 

 oxalate crystals and volatile oil globules. 



FUNCTIONS OF PRIMARY STEM TISSUES 



The functions of the different structures present 

 in primary stems may be summarized as follows: 



Covering tissues . 



Supporting tissues . 



Primary epidermis, 



Triohomes, 



Hypodermis. 



Bast fibers, 

 Wood fibers, 

 Stone cells, 

 Collenehyma, 

 Endodermis. 



Absorbing tissues Stomata. 



Assimilating and r Chlorophyll in hypoderm layer, 



Parenchyma, 

 Glandular hairs. 



issimilating and r Chlorophyll ir 



synthesis tissues j Parenchyma, 



I Glandular hai 



{Sieve tubes, 

 Ducts, 

 Porous parenchyma. 



, „. ( Cortical parenchyma, 



Storage tissues { „.,, , ' , 



I Pith parenchyma. 



Meristematic tissues Cambium. 



SECONDARY STEM STRUCTURES 



Secondary stem structures are present in mature 

 dicotyledonous plants. They represent the permanent 

 tissues of this class of plants and are found in woody 

 stems. The changes occurring in the transition from 



