LABORATORY MATERIALS ON PRIMARY XYLEM
AND VASCULAR CAMBIUM

 

 

                In this lab we will be examining primary xylem first in macerated form, and then in both cross-section and longitudinal section.  In each case, find the primary xylem, note its location and structure, and try to distinguish proto- and metaxylem (when possible).  Some of the same materials may be used for vascular cambium observations as well.

 

 

I.            Primary Xylem:

 

1.             Apium, celery:  partially macerated vascular bundles from the petiole.  Transfer 1-2 segments onto your slide and gently tease apart with needle tools.  Stain with methylene blue, add a cover slip, and observe.  (These strands were boiled in 2% KOH for about 15 min and then washed.)

 

2.             Trifolium, clover:  prepared slides of XS and RS stem.

 

3.             Zea, corn:  prepared slides of XS and RS stem.

 

4.             Cucurbita, gourd family:  demonstration slide of LS vascular bundle in stem internode.

 

 

II.            Vascular Cambium -- Herbaceous plants  (prepared slides):

 

1.             Trifolium, clover -- XS young stem for fascicular cambium.  Look for interfasicular cambium as well, which may be present in some slides.  Recall that you have seen this slide before.  Make sure you can identify all parts of the vascular cylinder.

 

2.             Medicago, alfalfa -- XS young stem showing fascicular and interfascicular cambium.

 

III.            Vascular Cambium --  Arborescent plant (prepared slides):  Identify the vascular cambium and note its structure.  How is it distinguished from the secondary xylem and secondary phloem in each type of section?

 

 

1.             Robinia, locust -- XS, RS & TS of old stem.  Look at the XS slide first, then the XRT slide.  Compare also with cross-section of young stem.

 

               

IV.              Fresh Materials:

 

1.                   Asclepias, milkweed -- Cut stem into cross and longitudinal sections.  Stain with IKI and Aniline Blue as for phloem tissues.  Identify the site of the vascular cambium.  Interpret the size and shape of the cambium cells.

2.                   Vitis, grape -- Cut young stems into cross and longitudinal sections and examine as per milkweed.  What differences are found in vascular cambium?

3.                   Parthenocissus, Virginia creeper -- Prepare as per milkweed.  Note the transition from vascular cambium to secondary phloem and xylem.