Autumn is in the air, and, in addition to cooler temperatures and porch pumpkins, that means The Detroit News Fall Perennial Exchange, which takes place 9 to 11 a.m. Saturday. New this fall is a collaborative effort among participating green thumbs, the Wayne State University Department of Art and Art History and the \"Heidelberg Project.\" To help landscape the \"Heidelberg Project,\" WSU needs donated perennials, in particular, orange butterfly milkweed, wild indigo, coreopsis, baby\'s breath, lupine, Russian sage, autumn joy sedum, feather reed grass, variegated maiden grass, smooth aster, flowering splurge, gray goldenrod and switch grass. You are invited to drop off these perennials at the WSU table at the exchange.