Why Do Cacti Have Spines? 

Source of pictures: Pixabay.com

In an art class, the teacher asked each student to draw a plant, and then show the picture to other students to let them guess what is on the picture. Holding a crayon in his hand, Daniel had no idea which plant to draw. Suddenly he thought of the sunflowers he saw with his mom last week. The dish-shaped flowers were very beautiful. Then he got an idea. He drew the petals of sunflowers with a yellow crayon and then the thin straight stems with a green crayon. Soon a sunflower was drawn on the paper. He looked at classmates around him and found Jessica was still daubing with a red crayon. It was probably a rose he guessed. Benjamin was drawing green columns with small yellow spines scattering over them. Daniel didn't know what they were. So he asked softly, "Hey, what are you drawing?"

Benjamin turned around and said, "Have a guess."

Daniel couldn't figure out what the strange shape was like.

"I'm drawing so well. Why can't you guess it?" Benjamin said anxiously.

"Why do I feel like I've never seen anything like those?" Daniel said in puzzled tones, "Are you sure you're drawing earth plants and not alien things in your dreams?"

Benjamin poked Jessica gently on her back with his crayon and asked, "Hey, look what I'm drawing?"

Jessica took a look and said, "Cacti, right? They are vivid with so many spines."

"Cacti?" Daniel heard the name for the first time.

Seeing Jessica knew what he was drawing at a glance, Benjamin was confident in his work. He said to Daniel, "You've never seen a cactus before, have you? It's easy to grow. You don't have to water or fertilize it every day."

Daniel still thought the plant looked strange and asked, "Do cacti look like this? They have many spines. Won't they prick themselves?"

Jessica answered in a whisper, "All cacti I've ever seen have spines. I don't know why."

Benjamin continued, "Maybe they are afraid of being eaten. My dog Thor never touches a cactus."

"Why don't other plants have spines? They should be worried about being eaten too," Daniel said with doubts.

Jessica responded, "Perhaps they have spines to protect their flowers from being picked, like the thorns on rose stems."

"Perhaps," Benjamin said, "But the cacti flowers aren't so pretty."

The teacher noticed their chatter and came over. Jessica and Benjamin quickly turned around and continued to draw. Daniel was still wondering why the cacti grew like fingers and had spines.

Before going to bed at night, Daniel's mom asked him if there was anything new at school today. He thought of Benjamin's painting and asked, "Mom, why do cacti have spines?"

"They aren't spines, but leaves. Cacti have lived in arid areas for a long time and evolved with needle-shaped spiny leaves to adapt to the arid environment. Generally, plant roots absorb water from the ground, but most of the water is lost through transpiration from the leaves into the air. The larger the surface area of a leaf, the faster the transpiration. It's similar to the way we dry our clothes under sun. If we unfold the clothes, they will dry faster. Otherwise, they will dry slower. Therefore, the needle-like spines of cacti can reduce transpiration and water loss and protect them from being eaten by animals."

Daniel was amazed because he had never known a plant could develop its leaves into needle-type spines for survival.

Author: Huang Jing