'Tar' the result of a 'find', preserving the directory structure

I want to tar all the *.txt file, that I get from the result of a find , that exist into a directory having a tree like this:

• Directory_name


• 
  
  
  
  • dir1
  
  
  
  


• 
  
  
  
  • 
    
    
    
    • file1.pdf
    
    
    
    
  
  
  
  


• 
  
  
  
  • 
    
    
    
    • file1.txt
    
    
    
    
  
  
  
  


• 
  
  
  
  • dir2
  
  
  
  


• 
  
  
  
  • 
    
    
    
    • file2.pdf
    
    
    
    
  
  
  
  


• 
  
  
  
  • 
    
    
    
    • file2.txt
    
    
    
    
  
  
  
  


• 
  
  
  
  • dir3
  
  
  
  


• 
  
  
  
  • 
    
    
    
    • file3.pdf
    
    
    
    
  
  
  
  


• 
  
  
  
  • 
    
    
    
    • file3.txt
    
    
    
    
  
  
  
  

(used name are just as example)

But I want to preserve the directory structure.

What is the command the could give me a tar.gz file with this content?

• dir1


• 
  
  
  
  • file1.txt
  
  
  
  


• dir2


• 
  
  
  
  • file2.txt
  
  
  
  


• dir3


• 
  
  
  
  • file3.txt