This week we looked at a few leaves belonging to plants that have adapted to survive the niche in which they found themselves. Waterlilies have adapted to survive floating atop bodies of water, the rubber plant has adapted to survive tropical and equatorial climates, and the oleander has developed advantages for surviving in very dry climates. The Nymphaea (waterlily) leaf has stomata on top of their leaves instead of below to allow for increased air exchange and nutrient exchange; they do not have a defense against transpiration as other plants do in the form of guard cells. The loss due to transpiration is not a primary issue for the waterlily since it has extremely good access to water. The sclereid labeled above is meant as a support for the leaf; it helps tent up the leaf which allows for greater air exchange in the leaf air space and provides flotation for the pad. The cuticle of the leaf is quite thin and helps repel water from the stomata. -Chris Barrett The sunken stomata of the Ficus plant helps the plant retain water. By not being flush with the rest of the epidermis, the stomata allow water vapor to be released yet not be immediately blown away by wind, therefore retaining an amount of water for reabsorption. The hypodermis is quite thick on top of the palisade mesophyll cells, perhaps for protection from intense UV radiation. The sub-stomatal regions are quite large, allowing for greater gas exchange in the mesophyll cells. There are not any trichomes visible on this leaf section. This large open areas in the spongy mesophyll, the sunken stomata, and the thickened hypodermis point to this plant being able to survive very hot, and very sunny climates, perhaps in the equatorial region of the world. -Chris Barrett The adaptations of the Nerium oleander plant have allowed it to survive in very dry climates. These are evident through the presence of stomatal crypts, which contain multiple stoma positioned far away from outer line of the lower epidermis. There are also trichomes present near the openings of the stomatal crypts. Both the presence of the stomatal crypts and the trichomes located inside of them point to adaptations for survival in very dry climates. The increased presence of plant fibers in the leaves allows the leaf to maintain its shape even when its other cells are plasmolyzed in dry spouts. Its multiple epidermis and thick cuticle allows the plant to handle high ultra violet radiation.
Regardless of the fact that every part of the plant is toxic to humans and other animals, it is one of the most widely grown plants in the world due to its drought-resistance with uses including ornamental, medicine, and wind-blocking. The oleander plant is also the official flower of the city of Hiroshima as it was the first plant to flower there after the destruction of the city by nuclear blast. -Chris Barrett
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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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