Riddle Me This: Earth Day Edition

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Across
  1. 1. riddle #16
  2. 3. tree, riddle #22
  3. 6. riddle #14
  4. 7. riddle #2
  5. 8. riddle #13
  6. 10. riddle #10
  7. 14. riddle #20
  8. 16. riddle #8
  9. 17. riddle #15
  10. 20. riddle #9
  11. 21. riddle #17
Down
  1. 2. riddle #6
  2. 4. riddle #1
  3. 5. riddle #12
  4. 9. riddle #4
  5. 11. riddle #7
  6. 12. riddle #18
  7. 13. riddle #5
  8. 15. riddle #19
  9. 17. riddle #11
  10. 18. riddle #21
  11. 19. riddle #3