Primary Growth: Stems and Leaves

Plant Growth and Development Apical Meristem – the main upward growth shoot of a tree or other plant. The Axillary Bud is the “insurance policy” that takes over if the original apical meristem is lost and becomes the new apical meristem. They can also form branches or flowers.

I. Apical Dominance When the original apical meristem is damaged, a new axillary bud takes over and creates a new apical meristem. New Apical Meristem already formed

Lateral Meristem The Lateral Meristem is the outward growth area of a plant. A woody plant leaves behind rings where this happens. These rings can be counted to determine the age of the plant. This tree, for example is 6 years old. It is important to remember to count the pith and the outer cambium layer.

Roots’ Meristems The meristem at the bottom of roots is also called an apical meristem. This is where we get a lot of the information we have about plant growth and development, due to it’s ease of study.

II. Phylotaxis Phylotaxis is the arrangement of leaves on a plant. They may be simple, or more complex. Road Trip (sort of!) Let’s look at some simple leaves; pinnate; bi-pinnate, and palmate leaves and then go out on the campus to locate examples of each!

A. Simple Leaves Lobes Simple leaves always have a single blade attached to the petiole. It is important to remember that leaves DO NOT have stems! Blade Petiole

B. Compound Leaves Pinnate leaves are once divided along the leaf petiole and rachis. Hickory is a good example of this.

Bipinnate Leaves Bipinnate leaves are twice divided along the leaf petiole and rachis. Mimosa is a good example of this.

Palmate Leaves Palmate leaves have leaflets that spread outward like the fingers of a hand, often in palms and other plants.

Perfoliate Leaves In Perfoliate leaves, the stem perforates the new leaves that develop around it. Honeysuckle is a really good example.

Peltate Leaves Peltate leaves are attached by the petiole directly to the center of the blade of the leaf. Example : lily pads

A peltate leaf looks like this underneath A peltate leaf looks like this underneath. I couldn’t find a photo that showed this!

Leaf Arrangements

Opposite Leaf Arrangement Note that the leaves are opposite each other on the branch at each node. A node is where leaves or flowers emerge from the branch. nodes Example : Red Maple

Alternate Leaf Arrangement In alternate arrangement, the leaves or flowers will be arranged on the branch at the nodes in a pattern alternating from one side to the other. nodes Example: Persimmon

Whorled Leaf Arrangement In a whorled leaf arrangement, the leaves radiate out from a single node. There may be many of them or just a few. Sinningia leucotricha

Venation

Net Venation Net venation spreads out from the rachis like the branches of a tree. Examples: sycamore; maple

Parallel Venation In parallel venation, the veins move along the blade in a parallel fashion, never spreading or branching. Example: corn

1. Is this leaf, simple or compound?

2. What kind of venation is displayed here?

3. What kind of leaf arrangement do we see here?

4. What kind of leaves are these?

5. What arrangement is this?

6. What arrangement is this?

7. What kind of edges does this leaf have?

8.What kind of leaf structure is this?

9. What kind of leaf structure is this?

10. What kind of leaf structure is this?

11.What kind of venation does this leaf have?

12. What kind of leaf structure is this?

13. What kind of leaf edges are found here ?