Defeating The Plant Boss:

The trick is to knock down the light-reflecting mirrors and bomb the plant away. At first, there is only one mirror that reflects the light and helps grow the plant. Fire at the Boss with normal fire rapidly until it is stunned; there is no need for heavy firearms. It will not be able to attack you at all if you stun it on time. After the plant Boss is stunned, run to the one reflecting mirror and shoot the red target behind the mirror with either a charge beam or only one missile. The plant will shrink and its spiky roots will vanish. Roll into a ball, go into where the roots were protecting, and drop a bomb. The plant is killed, but returns with two mirrors. Do the same thing with two mirrors, then three mirrors, then finally four mirrors. After finally killing the plant, the Varia Suit is yours.