Blog by Max McDonald Week 5 already in the books!! Wow the term really does fly by when your having so much fun learning about plant structure and botany with Dr. LP! Any way get ready to learn about some leaves and grass for your cat. First things first, whats up with these leaves? Just bud + leaf? simple right? Wrong! In the above image we see an example of a compound leaf. Compound leaves form from the same place as simple leaves, axillary buds. Compound leaves are made up of a petiole, that stems from the shoot, and multiple leaflets growing directly from the petiole. It is easy to mistake leaflets for leaves, but don't be deceived by their similar form and function! Leaflets come in clusters, on petioles, while leaves come directly from the shoot, one petiole to one leaf. I took the above image in class last Thursday. You can clearly see all of the the features that make up a compound leaf. A petiole stemming from an axillary bud, 5 leaflets stemming from the petiole, the bud sitting above the petiole, and even some axillary prickles! ouch! I could talk about compound leaves all day! so cool ! but, there are more pressing leaves at hand now that you are informed about the complex ones. Buckle up. I bet your wondering about the arrangement of leaves on a stem or axis. me too. If only there was a word for that...Well, I hope you buckled up, because guess what? There is. Phyllotaxy comes in many different forms, but in the interest of brevity, i'll only enlighten you with two. Firstly there is opposite phyllotaxy. In opposite phyllotaxy the axillary buds stem from opposite sides of the stem, just like in the below picture. Secondly there is alternate phyllotaxy. Unlike opposite phyllotaxy the axillary buds in alternate phyllotaxy's alternate down the stem. This leaves open space directly across from and bud on the shoot. The image below is an example of some alternate phyllotaxy on a piece of english ivy from lab. When is this guy going to get to the catgrass?! Don't worry, right MEOW! Below is an example of a cross section of the aforementioned grass for your cat, more commonly known as wheat grass, a C3 grass. You can see the upper epidermis, which uses translucent cells to focus light into the mesophyll cells. Also visible in the middle of the cross section is a vascular bundle. At the very bottom of the cross-section is a stoma. The stoma is a pore in the grass that allows for greater absorption of CO2. The stomatal pore is opened and closed by guard cells on each side. The CO2 enters the stomatal pore and absorbed by the water that surround the mesophyll cells. Check out the stoma and guard cells visible is this epidermal peel below! interesting and beautiful!
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Submitted by Tyler Hardy In this week’s lab, we took a close look at the characters of woody twigs of vascular plants. It may not seem like it initially, but there is a lot going on with these complex pieces of anatomy! These multi-faceted structures play an important role in several different plant functions, including water and nutrient transport, gas exchange, structural integrity, and new growth. Each twig has a variety of different organs present to be able to perform these duties; check it out! First, lets take a glance at a few twigs from different species, then we can break down what we are looking at. At the very tip of a twig, you can find the terminal or apical bud, enclosed within bud scales for protection. This is where the newest growth of this branch or twig happens. You may find similar, smaller structures to the sides of this and along the stem in areas known as axils. These are the axillary buds; from these buds, a plant may develop smaller vegetative or reproductive shoots. Just below each axillary bud, there is the leaf scar (or a leaf, depending on the plant and time of year), on the node where the leaf once was attached to the branch. The spaces between each node are called internodes. Within each leaf scar, notice the very small pores. These are the vascular bundle scars, the remnant of the vascular structures which once ran to and from the leaf. Following a twig lengthwise, you may notice how it maybe segmented by annular rings. These rings are the bud scale scars, what’s left from last year’s apical bud, and the space between each represents one year’s growth. All along the twig, look for small pores called lenticels. These help to provide gas exchange through the thick, protective bark that covers the woody parts of plants. And that’s just on the surface! Inside each twig are layers of protective tissues, photosynthetic tissues, structural tissues, and vascular tissues, all highly organized and intricately connected for maximum efficiency. So, next time you are picking up sticks in your yard, playing fetch with your dog, or just snapping twigs while you idle, try to remember what complex pieces of biological machinery it is that you are handling! |
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