A light routing puzzle in Pop's glasshouse. Sun comes through a gap in the shadecloth, and every mirror on the bench can be turned one of two ways: point the beam at every seedling and the house is fed. Cracked panes split a beam in two, stacked pots drink it, coloured glass turns white light red or green or blue, and two colours arriving together add up, so a seedling that wants yellow needs red and green at once and refuses anything else. Forty houses, no clock, nothing to lose, and every one of them has a proven shortest answer to chase once you have found an answer at all.