What is depicted by "$X$" and "$Y$" in the following diagram?

• A
  $X$ - Plumule, $Y$ - Cotyledon
• B
  $X$ - Plumule, $Y$ - Root cap
• C
  $X$ - Root cap, $Y$ - Radicle
• D
  $X$ - Radicle, $Y$ - Root cap