Question

The following diagrams show the types of secondary thickenings in the xylem vessels. Identify the types labelled from A to E. Choose the correct option from the given options.

• A. A- annular, B-spiral, C- scalariform, D- reticulate, E- pitted with border
• B. A- annular, B-` spiral, C- scalariform, D-pitted with border, E- reticulate
• C. A- spiral, B- annular, C- reticulate, D- scalariform, E- pitted with border
• D. A-spiral, B- annular, C- scalariform, D- reticulate, E- pitted simple

Answer 1

Answer: (A)

The secondary thickenings occur due to deposition of lignin on the secondary walls in various forms. The ability for plant cells to make secondary cell walls is considered to be one of the most important evolutionary feature for vascular plants. Secondary cell walls in tracheary elements provide mechanical strength to plant organs. The lignin in tracheary elements are deposited in specific patterns of helical, annular, scalariform, reticulated and pitted patterns. The spiral pattern is mostly found in the pteridophytes, and pitted or bordered-pitted generally occurs in gymnosperms.

So, the correct option is option B.