Phytochrome pigments in buds measure day length to time spring growth

Evidence

The fact is, Maples have a far more sophisticated system for detecting spring than we do. There are photosensors by the hundreds in every single bud, packed with light-absorbing pigments called phytochromes. Their job is to take the measure of light every day. Tightly furled, covered in red-brown scales, each bud holds an embryonic copy of a maple branch, and each bud wants desperately to someday be a full-fledged branch, leaves rustling in the wind and soaking up sun. But if the buds come out too soon they’ll be killed by freezing. Too late and they’ll miss the spring. So the buds keep the calendar. But those baby buds need energy for their growth into branches—like all newborns, they are hungry. — Robin Wall Kimmerer, Braiding Sweetgrass, 217

Categorization

• ADDENDUM: Connects to the Grafting & Growth essay’s treatment of trees as underused, sentient-seeming infrastructure — here the mechanism (phytochromes as photosensors) grounds bud timing in measurable physiology.
• XREF: connects to: Mosses grow black and crusty in sun because anthocyanin shields them from UV — Robin Wall Kimmerer, Gathering Moss: A Natural and Cultural…, 518

Broader Connections

• Mosses grow black and crusty in sun because anthocyanin shields them from UV #complicates (0.70) — Robin Wall Kimmerer, Gathering Moss, 518