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Evolution of Vascular Tissues, Vascular Tissue, Hydroid, Leptoid, Moss,…
Evolution of Vascular Tissues
Hydroids
water-conducting parenchyma cells
similar to tracheids but lack lignin and secondary wall thickenings
usually
thin-walled
lack helices
lack other thickenings
collapse during water stress
Leptoids
food-conducting parenchyma cells
very similar to phloem sieve cells
has an elongate shape and slightly oblique end walls
distinct in vertical section
Mosses
has no true vascular tissue
hydroids and stereids are important to function
hydroids
undergo several modifications
are dead at maturity
stereids
elongate, thick-walled, slender, and fiber-like cells
add support to the stem
typically arranged in a cylinder around the hydrome
Lycophytes
also known as spike mosses, or quillworts
earliest group with true vascular tissue
has a dominant free living sporophyte stage
Monilophyta
diverse group including
whisk ferns
horsetails
ferns
well developed vascular tissue is found throughout the monilophytes
Vascular Tissue
essential functions
delivery of resources
mechanical support
communication within the plant
higher amount of degrees of modifications
examples of vascular cryptograms
lycophytes
pterophytes
had major impacts on evolution of terrestrial biology
