A story arc from October 2nd to October 21st of 1995.
Calvin and his classmates are assigned to collect fifty leaves over the course of two weeks by Miss Wormwood, with each leaf being a different kind (so you can't have multiples of the same type of leaf). Calvin was upset about the assignment, feeling it was stupid and pointless -- Hobbes tried getting Calvin to get started on it right away, but Calvin (being who he is), ultimately put it off until the absolute last possible minute. Susie Derkins was already almost done with it by the halfway mark, unlike Calvin, who still hadn't gotten started on it.
Calvin ultimately doesn't bother getting started on his leaf collection until the day before its due -- specifically, he tries getting his mom to take him to the local arboretum just as she's getting started on making dinner the night before it's due. While he's outside collecting leaves with Hobbes, Calvin blames his mom for his poor performance in school -- but Hobbes comes to her defense by pointing out that it's Calvin's own fault, due to his habit of always putting assignments off until the last possible second, though Calvin refuses to listen.
While they're collecting, the duo's approached by a UFO piloted by a pair of aliens named Galaxoid and Nebular, who want to take over Earth -- pretending to be the planet's ruler, Calvin agrees to it as long as Galaxoid and Nebular give him a collection of fifty different tree leaves from their home planet (the aliens agree to this, assuming that humans use leaves as currency). Calvin makes them promise to come back by 8pm with the collection, and the two aliens rush off to get their assignment done -- they come back much later than expected, but Calvin and Hobbes meets them out in the yard to get the leaf collection from them. But Calvin's Dad finds him and Hobbes and, not realizing what Calvin had done, makes them go back to bed.
Calvin presents his collection the next day in school -- but of course, nobody believes that the leaves came from another planet and Calvin, predictably, fails the assignment.
While taking a walk through the woods, Calvin's complaining about what happened, feeling that Miss Wormwood refuses to acknowledge that the assignment was "pointless" and that information about leaves is "useless knowledge" (even grabbing a leaf from a random tree/shrub for emphasis). But then Hobbes points out that the leaf Calvin just grabbed was poison sumac (which will obviously give Calvin a nasty rash, as it contains urochiol, also occurring in poison ivy and poison oak).
- When Calvin showed his project to Susie (prior to showing it in class), this is how she described his leaf collection, "It looks like you took fifty maple leaves and cut them into weird shapes."