PHILANTHROPY AND PHILODENDRONS
The Basics: Cell Types
Primary Meristem
Tissue System
Tissues
Cell Types
Protoderm
Procambium
Ground Meristem
Dermal
Vascular
Ground
Epidermis
Xylem
Phloem
Parenchyma
Collenchyma
Sclerenchyma
Pavement cells, guard cells, trichomes, etc.
Vessel elements, sieve tube members, etc.
Sclereids, fibers, storage parenchyma, etc.
Right off the bat, I thought I would go ahead and put a simple chart of how the different cell types correlate to the different tissue and primary meristem types because I found this incredibly useful when I was first learning about this topic. Feel free to come back to this as you read because I promise it will provide great clarity. However, it should be noted that there are a number of cell types for each primary meristem, but I only included a few for the sake of space. I will add a full list of all the cell types in each primary meristem as I go over each of these topics.
I also want to address the fact that this chart only covers tissues and cell types that are derived from the primary meristem of a plant. This means that it only composes the herbaceous parts of the plant, while everything that is derived from the secondary meristem will be discussed in a later article. Tissues and cell types derived from the secondary meristem are woody, or lignized.
Epidermis
Figure 1: Longitudinal section of a Lonicera species apical meristem at 100x magnification.
The first tissues I am going to get into are the dermal tissues. The root word derm- means 'skin,' which is why a person who studies skin is called a dermatologist. Therefore, the dermal tissues of a plant are pretty much the plants skin, or the outer layers of cells particularly on the stems, leaves, and roots.
As shown in the chart, the primary meristem the dermal tissue system is derived from is called the periderm. This periderm exists as the outer most cell layer at the parts of the plant that maintain undifferentiated cells, such as the shoot apical and axillary buds, and root apical and axillary buds.
There are many different kinds of cells that compose the dermal tissue system. A few of the most well known ones are pavement cells, guard cells, subsidiary cells, and trichomes. In Figure 2, you will see that the pavement cells look kind of like puzzle pieces and they are kind of the 'filler' cells of the epidermis. It is important to note, however, that pavement cells do not always have a puzzle piece shape to them. You will notice in further photos that they can be rounded, rectangular, and also completely random in shape.
You will also see that the guard cells and subsidiary cells go together. This is because, together, they compose the stomata that are key for the entire cohesion-tension mechanism of the xylem.
Another thing to keep in mind is that there are different kinds of guard and subsidiary cell arrangements. The most common arrangements include anomocytic, anisocytic, diacytic, and paracytic.
Subsidiary Cell
Guard Cell
Pavement Cell
Figure 2: Paradermal section of a Jatropha purpurea at 400x magnification.
Paracytic stomata have subsidiary cells that are aligned with the guard cells, like those shown in Figure 2. Diacytic stomata have subsidiary cells that are misaligned, or perpendicular to the guard cells, as shown in Figure 3.
Anomocytic stomata have subsidiary cells that are entirely random in their positioning in reference to the guard cells. These stomata are shown in Figure 4.
The final stomata, anisocytic stomata, always have three subsidiary cells with one being slightly smaller than the other two. You can see anisocytic stomata in Figure 5.
Moving forward, trichomes are another hugely important aspect of epidermal anatomy. Trichomes can be unicellular, multicellular, stellate, glandular, branched, and so much more.