Bidens pilosa secondary xylem
This image shows part of a the differentiated and
undifferentiated secondary xylem in a Bidens stem. Notice the
large xylem vessel next to the cambium, which, at this stage, lacks
secondary wall development (it therefore also lacks lignin at this
The smaller tracheary elements (tracheids mostly) show stages of lignification of their secondary walls. Not how the lignin is being deposited mostly in the corners for these cells first.