What is it?

[Marty Reichenberger <mreich@terraworld.net>]

We are in the middle of poinsettia propagation.  I have Freedom that are
at the callusing stage.  Amongst the white callus tissue, I can see
black streaks, and some stems are streaked about 1/2" upward into the
leaf petiole (basically just the portion of the stem in the Oasis).  I
noticed the same thing last year and had ZERO rot in the cuttings.  It
looks just like they are getting some rot started in them, but they look
terrific and go ahead and root just as fast as one's with no "funny"
black tissue.  Does anyone else know what causes this, or what this is
just for my peace of mind??  I am honestly not afraid of losing any,
because they do this every year, but I would like any thoughts on the
subject!!

Thanks!
Marty Reichenberger
Green Thumb Greenhouse
Independence, KS