Elm, say, planted in stone in part of city (6)
I believe the answer is:
street
'part of city' is the definition.
(cities have lots of streets)
'elm say planted in stone' is the wordplay.
'elm say' becomes 'tree' (elm is a kind of tree).
'planted in' means one lot of letters goes inside another.
'stone' becomes 'st'.
'tree' going within 'st' is 'STREET'.
'in' is the link.
(Other definitions for street that I've seen before include "Town road" , "Perry's Della" , "Urban thoroughfare" , "Built-up road" , "Urban road" .)