Answer:
Alright love, it would be - mast cells
 
        
             
        
        
        
The primary source of stem thickening in plants is the vascular cambium. It is a plant tissue located between the phloem and the xylem and in the root of a vascular plant. It is the source of secondary growth or the radial growth of the stem of a plant.
        
             
        
        
        
This answer to this question is c