### Clue: Nitrogen does spread over tops of underground lumps — these? (7)
### Answer: NODULES 
 ### Explanation: Definition: these
 N(symbol for the chemical element, nitrogen) + **anagram of**(… spread) DOES **containing**(over) **the 1st letters, respectively, of**(tops of) "underground lumps ".
Defn: …, lumps, that is.