Practice question

Origin of tracheids with lignified secondary walls solved two critical constraints for land colonization simultaneously. Hydraulically, they enabled efficient apoplastic water ascent under negative pressure generated by transpiration, sustaining tall aerial shoots despite absence of true roots initially assisted by capillary action and rhizoids. Mechanically, lignin confers compressive strength and resistance to collapse allowing upright growth, increased height, branching, improved light interception and canopy formation. This dual role in conduction and skeletal support facilitated evolution of complex sporophytes and Devonian forests.