Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Series # | Season # | Title | Directed by: | Written by: | Original air date |
| --- | --- | --- | --- | --- | --- |
| 53.0 | 1.0 | "Through the Time Barrier" | Harry Gerstad | David Chantler | April 23, 1955 |
| 54.0 | 2.0 | "The Talking Clue" | Harry Gerstad | David Chantler | April 30, 1955 |
| 55.0 | 3.0 | "The Lucky Cat" | Harry Gerstad | Jackson Gillis | May 7, 1955 |
| 56.0 | 4.0 | " Superman Week" | Harry Gerstad | Peggy Chantler Dick | May 14, 1955 |
| 57.0 | 5.0 | "Great Caesar's Ghost" | Harry Gerstad | Jackson Gillis | May 21, 1955 |
| 58.0 | 6.0 | "Test of a Warrior" | George Blair | Leroy H. Zehren | May 28, 1955 |
| 59.0 | 7.0 | "Olsen's Millions" | George Blair | David Chantler | June 4, 1955 |
| 60.0 | 8.0 | "Clark Kent, Outlaw" | George Blair | Leroy H. Zehren | September 10, 1955 |
| 61.0 | 9.0 | "The Magic Necklace" | George Blair | Jackson Gillis | September 17, 1955 |
| 62.0 | 10.0 | "The Bully of Dry Gulch" | George Blair | David Chantler | September 24, 1955 |
| 63.0 | 11.0 | "Flight to the North" | George Blair | David Chantler | October 1, 1955 |
| 64.0 | 12.0 | "The Seven Souvenirs" | George Blair | Jackson Gillis | October 8, 1955 |
Question:
Who directed the episode that was written by Jackson Gillis and Originally aired on May 21, 1955?
Answer:
Harry Gerstad