Not all plants have stems. Some plants like dandelions just have leaves. These plants can’t get very big. Stems come between the roots and the leaves letting a plant get big. Let’s see how a stem does this.
Question: How does a stem let a plant get big?
1 pumpkin side vine about 1.5 m long
Jar of water with lots of food coloring (red or blue) in it
Step 1: Open your Science Journal, write “Investigation 12” and the date.
Step 2: Cut a side vine off a pumpkin vine
Step 3: Cut off a section of the stem with a leaf on the top end. Put the stem in the jar of water and set it aside overnight.
Step 4: Examine the rest of the side vine. What does it feel like? How long are the stem pieces (internodes) between leaf petioles? What shape is the stem?
Step 5: Cut off a piece of stem from between two petioles to examine. Is it solid? Is it the same diameter at both ends? Is it the same all the way around? Try to tear it across. Try to tear it lengthwise. Does the inside feel the same as the outside? What else do you see?
Step 6: Examine the strings and soft parts with the magnifying glass. How many strings are there? Are they all the same? Try to cut some strings lengthwise to examine. [Be very careful not to cut yourself.]
Step 7: Cut open a section of vine so you can see how a leaf petiole joins the stem. Examine how the strings go from the stem into the leaf.
Step 8: Carefully cut off a tendril and examine it. What does it feel like? Is it hollow? Try to cut it lengthwise and see what is inside it. [Do this carefully.]
Step 9: Carefully cut off a white area from the stem below a leaf (the adventitious root) and examine it. How is it different from the stem?
Step 10: Examine the 5cm at the tip of the vine. Is it like the rest of the vine? What is found at the tip? Carefully cut the parts of the tip open to see what is inside.
Step 11: Examine flower buds on the vine by a leaf. Are the stalks like the vine? Do the cords go into the flower stems? Carefully cut open the flower buds. What is inside the buds?
Step 12: Take the piece of vine out of the food coloring. Cut across the end of the stem above where it was in the water. Can you find food coloring inside the vine?
Use this section to write down and draw what you see.
Petiole, Tendril and Stem:
Root and Stem:
Stem cross section plain (top) and food coloring:
Leaves from the very tip to 5cm back:
Tendrils from the very tip and 5cm back:
Male Flower from tip whole (top) then cross section:
Female Flower from tip whole (top) then cross section:
Compare tearing the stem across and lengthwise. Which way was easier? Why is this way easier?
What do you think the cords in the vine stems do?
How does the cord pattern change around the petiole? Why do you think the pattern does this?
How do the cords affect how the stem crushes?
What are the advantages of a hollow stem to the plant?
What are the disadvantages of a hollow stem to the plant?
Where are the spines found on the stem? What do the spines do for the plant?
Why are the parts so small at the tip of the vine?
How do you think they get bigger? How can you test your idea?
Compare the growing tips of the sprout [from Investigation 10] and the vine. Why do you think a plant only grows longer at the tips?
How does a pumpkin plant use tendrils? Why is this important to the plant? [You can go out and look at the tendrils on your pumpkin plant.]
Look back at Investigation 10. How has the stem changed from that of a sprout?