Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Secondary growth in the Arabidopsis hypocotyls. Toluidine blue stained, freehand sections differentiate between the lignified cell walls (blue) and the primary walls (red). Two distinct stages of development are marked (I and II). In the first phase only vessels are formed, whereas in stage II both vessels and fibers are formed.
