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.
Overturning Presidential Veto. While the president has the right to veto a bill, Congress in turn has the power to override the president's veto. To do this, two-thirds of both the House of Representatives and the Senate must vote in favor of the override.