Lab 4 - Stems: Structure and Function

SHOOT SYSTEM: STEMS

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A square stem of a Coleus plant. The aerial part of the plant is the shoot which includes the stems as well as the leaves. *look into lab 5 blog posting for information on leaves. 

The specific regions where leaves, buds and breaches arise are called nodes. The stem connecting two nodes is the internode.

Two halves of a bean seed minus its seed coat. When the seed germinates the cotyledons become two embryonic leaves, the radicle grows into the embryonic root and the plumule develops into the shoot.

A longitudinal section through the shoot tip of Coleus prepared slide. A magnified version of the red box is in the next picture. Can you name the following terms without looking into your notebooks? Protoderm, ground meristem, procambium, Leaf primordium, apical meristem, trichome and bud primordium. Scroll to the middle of this page to find the answer.

The photo from the red box above. These are scalariform vessels and tracheids of the xylem. However, they look more helical/spiral than sclariform.

Prepared slide stem cross section of Ranunculus (buttercup). Buttercups have closed vascular bundles meaning all of the procambial cells have differentiated (ie. are all used up). They do not exhibit secondary growth because no further differentiation is possible. Note the parenchymatous cortex and pith. The vascular bundles are located in a circle in the stem. The primary phloem is to the outside and the primary xylem is to the inside. The division of the xylem is from the inside out and thus the the development is endarch. 

The above a stem cross section of Riciinus (castorbean) that is starting secondary growth. The layer of cells outlined in red is the interfasicular cambium. Above this layer are clusters of phloem tissue and the large cells below are xylem vessels. 

Here is zoomed out view of the interfasicular cambium.

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Labeled longitudinal section of Coleus. The location of the bud primordia is also known as the axil. The outer several layers of the apical meristem is the tunica layer and underneath this layer is the corpus layer.

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Stem cross section of Sambucus. If this picture were to continue inward, it would show the primary xylem at the end of the secondary xylem. And further inward would be the pith.

Didn't get a good section of Pelargonium.  : (

Prepared slide of Tilia (basswood) stem cross section.

Prepared slide of Zea mays (corn). Corn is a monocot and do not engage in secondary growth (characteristic of monocots). It has its vascular bundles scattered throughout its stem.


-MIDY