Through the northern fall they worked around the glacier, and saw the days grow shorter, and the winds colder. Big intricate ice flowers grew on the glacier every night, and only melted at the edges briefly in the midafternoons, after which they hardened and served as the base for even more complex petals that appeared the next morning, the small sharp crystalline flakes bursting away in every direction from the larger fins and tines beneath. They could not help crushing entire fractal worlds with every step as they crunch-crunched over the ice, looking for the plants now covered in frost, to see how they were coping with the coming cold. Looking across the bumpy white waste, feeling the wind cut through one of the thicker insulated walkers, it seemed to Sax that a very severe winterkill was inevitable.

But looks were deceptive. Oh there would be winterkill, of course; but the plants were hardening, as the overwintering gardeners called it, acclimatizing to the onset of winter. It was a three-stage process, Sax learned, digging in the thin hard-packed snow to find the signs. First, phytochrome clocks in the leaves sensed the shorter days— and now they were getting shorter fast, with dark fronts coming through every week or so, dumping dirty white snow out of black low-bellied cumulonimbus clouds. In the second stage, growth ceased, carbohydrates translocated to the roots, and amounts of abscisic acid grew in some leaves until they fell off. Sax found lots of these leaves, yellowed or brown and still hanging from their stems, hugging the ground and providing the yet living plant with some more insulation. During this stage water was moving out of cells into intercellular ice crystals, and the cell membranes were toughening, while sugar molecules replaced water molecules in some proteins. Then in the third and coldest stage, a smooth ice formed around the cells without rupturing them, in a process called vitrification.