Final answer:
The claim is false; while xylem is rigid and can fossilize, phloem does not fossilize as readily due to its structure composed of living cells.
Step-by-step explanation:
The statement that both xylem and phloem fossilize because they are rigid in structure is inaccurate. While xylem, the plant tissue responsible for water and mineral transport, has a tendency to fossilize due to its rigid structure reinforced by lignin, phloem is less likely to undergo fossilization. Phloem, which facilitates the transport of organic compounds like sugars in plants, is comprised of living cells when mature and possesses a less rigid structure compared to xylem.
The process of fossilization typically involves the preservation of more durable structures, and xylem's lignin-reinforced rigidity contributes to its preservation in the fossil record. The lignin in xylem imparts strength and resistance to decay, making it more likely to withstand the fossilization process. Conversely, phloem, composed of living cells and having a weaker structural composition, is more susceptible to decomposition and less likely to be preserved in the fossil record.
During fossilization, soft tissues of plants often decay and are lost, leaving behind the more resistant and durable structures like lignified xylem tissues. While the rigidity of xylem plays a crucial role in its fossilization, this characteristic does not apply to phloem, which, due to its different function and cellular composition, is more fragile and less prone to preservation in the fossil record. The distinct properties of xylem and phloem highlight the complexity of plant tissues and their varied fates in the geological history of the Earth.