Below is a series of pictures of a eudicot stem tip (I.s.), Coleus sp. Much of what plant biologists have learned about leaf development has occurred by studying stem tip genetics. 40x (Ls-) Make a sketch of the 40x stem longitudinal section and upload it here with the following structures labeled: apical meristem, leaf primordium, axillary bud, procambium, vascular tissue (need to look lower down the stem for these sub-tissues), ground meristem, cortex; pith.
The Correct Answer and Explanation is:
Here is a sketch of a longitudinal section (L.S.) of a eudicot stem tip (Coleus sp.) at 40x magnification, with the required structures labeled:
[Image Placeholder: Sketch with labels]
Since I cannot draw or upload sketches directly into this message, I will describe the drawing so you can sketch it yourself or verify against your image:
How to Sketch:
- Start with the stem tip at the top center of your drawing.
- Draw the dome-shaped apical meristem at the very tip.
- Beneath and to the sides, draw two small bulges that represent the leaf primordia.
- At the base of each leaf primordium, draw a small bud-like structure: these are the axillary buds.
- Below the apical meristem, sketch vertical strands running downwards: these are the procambium.
- The vascular tissue (xylem and phloem) develops from the procambium and should be shown lower in the stem section.
- Surrounding the procambium, draw the ground meristem, a mass of cells filling the space around developing tissues.
- Towards the outer edges, show a zone of loosely packed cells: this is the cortex.
- In the center of the stem section, draw a circular region: this is the pith.
Explanation
The longitudinal section of a eudicot stem tip, such as that of Coleus sp., provides an essential view into plant development. At the very top of the stem is the apical meristem, a region of actively dividing cells responsible for vertical growth. This meristem produces new cells that will differentiate into various tissues of the plant.
Just below the apical meristem, small lateral bulges known as leaf primordia begin to form. These will develop into mature leaves. At the base of each primordium, a smaller outgrowth forms the axillary bud, which can potentially become a new branch or flower.
As cells divide and differentiate downward from the apical meristem, they form distinct zones. The procambium is one of the primary meristems, giving rise to the vascular tissues—xylem and phloem—that are critical for water and nutrient transport. These tissues become more distinct farther from the tip.
Surrounding the procambium is the ground meristem, which differentiates into the cortex and pith. The cortex lies just beneath the epidermis and functions in support and storage. The pith occupies the central part of the stem and is composed of parenchyma cells, primarily used for storage and sometimes for transport in young stems.
Together, these structures demonstrate how new organs and tissues emerge through a coordinated developmental process, starting from the apical meristem and leading to the formation of a functional stem capable of supporting leaves, transport, and growth.
