For those who want to take care of houseplants but can hardly take care of themselves, The Green Dumb Guide to Houseplants is the perfect handbook for even the most greenery-inept individual.   We all love the idea of houseplants, and maybe you've stood by helplessly as a cactus went all slimy or you've endured the perpetual indoor autumn of an unhappy Ficus. Good newsall of the plants in this book have two things in common: They're easy to find and hard to kill. The benefits of plant ownership are legion. Studies indicate just being around plants creates a relaxing effect on people. And plants make great roommatesno Peace Lily will ever criticize you for quitting your workout video to go finish a box of Triscuits.   Does your bedroom have a mattress on the floor and Christmas lights taped to the wall? Put a Money Tree in the corner. Instant upgrade! Are you a corporate lackey trapped under fluorescent lights and a drop-tile ceiling? A colorful Calathea or a chunky little