Why call this hat Xylem? The lacy eyelets and other design features reminded me of xylem under a microscope (see here, or check out the Google image search results)! It all seemed to click into place, since the color of this lovely yarn is called Sap -- enjoy!

Errata:

• Round A should be: #K2tog, yo, k1, yo, ssk, k3#.

• The very last crown dec row (8) should be: K2tog, k1, #k2tog, k2# (20 sts remain).