The lignified cells in the tendril's fiber ribbon glow bright blue under ultraviolet light. The thickened cell walls are clearly visible in the bottom two images. Disclaimer: AAAS and EurekAlert!

Overall, only 2.1% of the pine trees’ rings and 1.3% of the juniper shrubs’ rings were blue; the cells which hadn’t lignified properly were mainly found at the end of growth rings ...

Overall, only 2.1% of the pine trees' rings and 1.3% of the juniper shrubs' rings were blue; the cells which hadn't lignified properly were mainly found at the end of growth rings, in latewood.

6. The hypodermal layer of the outer surface of the sheath becomes first suberized, then lignified, as the sheath is pushed toward the exterior of the pseudostem. 7. The protoxylem elements of sheath, ...

‘Blue’ tree rings, which indicate that the cell walls of that year’s growth never lignified properly, show us when a summer was too cold for the plants to grow. The scientists identified blue rings ...