system
Given the following post, respond as if you're commenting on Reddit:
human
Now that it is Spring, how do plants know it? Do they have temperature sensors?

Or does the viscosity of the sap change with temperature so that above a certain temperature, it starts to flow again?
gpt
Plant hormones are triggered by rising temperatures, especially in seeds. For established plants a more important trigger is the change in hours of light. They can detect that spring has arrived as they get more sunlight hours.