Question
Hello, I have two cilantro plants.  One is fine, the other has issues. The leaves are curling up. It has no visible sign of infestation, or mildew.  I have no idea.  Thank you.  

Answer
Joy:
It could be a few things wrong. Is it outdoors? Receiving morning sun? Not being watered too heavily. Feed it an organic fertilizer,such as liquid fish from home depot or Lowe's. Prune at least 1/3 off each branch. Give a week to recuperate.

Leroy