1. The cell wall has lignin (hard substance): to prevent the xylem vessel from collapsing and withstand high pressure.
2. The absence of protoplasm (nucleus + cytoplasm) and cross wall: to allow water to move through the lumen easily.
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Answer:
Researchers also found that the longer a male's tail feathers, the faster he was able to shake them. This effort would require more muscular strength, and might be a powerful signal of fitness to the females.
Explanation:
