Cucurbits are monoecious; there are separate male and female blossoms on the same plant. The male flowers tend to open first, followed by the female flowers. It is only when both the male and female flowers are open that pollination can occur.
There is nowhere in the Constitution that says that the Congress can subpoena the President of the U.S. or his people. Congress does however have general subpoena powers, but they are not absolutely clear. There are Supreme Court cases that speak to this. They generally limit this to national security type of issues.
Of course the President can pardon himself. He is, after all, the executive, part of whose constitutional duty under Article 2 is to bring prosecutions and punish the guilty. You can't jail the head jailer, and you can't prosecute the head prosecutor's boss, unless he allows it.