Lab 9 - Secondary phloem and periderm

These are images of sections made by students in the lab on secondary phloem and periderm tissues

This image shows phloem tissues from the cottonwood stems.  You can see the general location of the phloem outside of the secondary xylem, but most of the tissues do not show clearly because the section was a little thick.  Note the clusters of phloem fibers staining very light blue.


This image (also cottonwood) is a little clearer.  The vascular cambium region is overexposed outside of the xylem on the lower-right of the image.  There are bands of phloem fibers in the secondary phloem and clusters of fibers further out into the cortex.  Beyond the cortex, the first periderm layer has formed.


This is a closer view of the cambium and phloem from cottonwood.  Most of the phloem parenchyma cells are filled with starch grains.


The phloem fibers and starch-filled parenchyma of cottonwood...


This image below shows the cambium region from live oak.  The cambium is running diagonally in the image from lower right to upper left.  The phloem would be to the lower left.  Xylem elements (the most recent are not lignified yet) are to the upper right.


Here is a section from live oak phloem.  The xylem runs across the top and so the center region would include cambium and phloem.  A group of thick-walled phloem fibers show up nicely towards the bottom of the image.  A ray passes along the right side, from the xylem and into the phloem, where is is just starting to spread (ray dilatation).


Here is a large, thick-walled sclerid in the secondary phloem, but I am not sure which species of plant.


Here is the outer stem region of a sycamore.  You can see the secondary xylem edge and then (outward) the secondary phloem.  Some thick fibers appear in the secondary phloem, but the large clusters of fibers might be from the primary phloem because the rays do not seem to extend out that far (remember, rays are made by the cambium, not in primary tissues like vascular bundles of primary xylem & phloem).  The wide rays of sycamore are also obvious in the xylem.


The next two images below show some interesting sclerids out in the cortex of a sycamore stem.



Here is an image from the outer regions of a sycamore stem.  The section was a bit thick to show some of the thinner walled cells clearly, but you can figure out where the tissues are located and the fibers and sclerids show up well.


Moving on to periderm, here's an image showing cottonwood periderm with phellogen and phellem layers.


These next two show mulberry periderm layers.



Lastly, these three images show the periderm of a sycamore stem.