In lab on Thursday February 16th we explored root structures of monocot and dicot roots. Our class examined a Corn plant to identify parts of the root. Monocot roots have adventitious roots where lateral roots give rise to fibrous roots. These type of roots do not have a primary root, but instead have many that branch out from the stem. Although the structure of the monocot and dicots are different, they still encompass the same internal anatomy. The image below on the left shows a picture of a Corn plant root through a microscope. The cross-section was stained with TBO and the microscope magnification is at 40x. The image on the right is a drawing of a monocot root with its labeled parts. The third image is another example of a monocot root structure. The epidermis layer of cells is found the outermost edge of the root and is the same for both monocot and dicot roots. In from the epidermis is the exodermis layer of cells (not labeled in on the image). Next is the cortex, which is made up of all the cells between the exodermis and the endodermis. The endodermis is the first, outermost layer of dark cells. The next layer of dark cells in known as the pericycle. The the larger bubble looking circles are the xylem cells. Surrounding the xylem cells are the phloem cells. The pith is the innermost cells from the xylem cells. Lastly, the stele is the area inside the endodermis cells.
By Keira Mitchell
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Oh man finally, I'm off of work. Now I can go to class and sit, I'm so tired of standing. Today's been a long day but now I have botany class! So here we are at lab and today's focus is about recognizing the tissues within stems and their functions, exploring the diversity of plant stems from different habitats, and seeing the difference between a monocot and a dicot plant. We did multiple cross sections of different types of plants. Let me tell you what! Cross sections are not easy. In order to get the best possible result you need to be able to cut the stem very thin. The problem for me is that my hand shakes too much, so it took me a couple tries to get a perfect cross section. One of my best cross sections is the broad bean stem, which can be seen in figure 1. This image was prepared and stained with Toluidine Blue O (TBO), and that's the reason we are able to see different colors and easily distinguish the different structures in this plant stem. The obvious thing you can notice between Figure 1 and Figure 2 is the complexity of a dicot structure. A distinct separation, that looks like a river that cuts through the forest, is called procambium. This separates the pith and the cortex of the stem. Not only that, comparing Figure 1 to Figure 2, their vascular bundle is very different from each other. In figure 1 you can see a separation between the xylem, which is responsible for transporting water and minerals, and the phloem, which is responsible for transporting food to the rest of the plant. But in figure 2 you can see that they're really close together, almost as if they were one. Now if we look closely at figure 1, you can see a blue stain on top of the phloem. That's what they call sclerenchyma, and we were told in class that this acts as a helmet and protects the phloem .
Now lets look at aquatic plants: Figure 3: These are images of a waterweed (Elodea). This is a cross section of its stem, and was stained with TBO. This image was taken under a compound microscope at about 40x. The second image is a zoomed in version of the first image. (Prepared and photographed by Taylor) The plant structure in land plants compared to aquatic plants is very interesting. I've always thought that since they are all plants, their insides looks the same. I'm obviously wrong. There is a big difference. In aquatic plants I was able to learn that they contain these huge, easily seen air spaces throughout the stem called aerenchyma. Looking at figure 3 above, you can see what I am talking about. These air spaces are very important to aquatic plants because it provides buoyancy and it allows easier circulation of gases. Now after this lab I should be an expert at distinguishing the aquatic plants and terrestrial plants just by looking at their cross sections. Author: John P.
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