Went from bryophyte dominated land scape and went up- vascular plants are now tallest all plants from vascular plants going forward have vascular tissue. Gymnosperms- advantages of height: light access (block competitors"" light by shading competitors, escape from competition for nutrients, better wind dispersal of spores. Modern trees have ring of dividing (growing) cells beneath the bark celled the vascular cambrium marrow somatic cells spur growth of plant. Produces new (lignified xylem up) and phloem (down-flow down) tissue. Xylem water and nutrients go up, phloem sugars flow down. Wood is made of dead secondary xylem/phloem - dead material still fortified with lignin (lignin gives wood its hardness) Tree rings- most pronounced in temperate climates more cells over summer and fewer in winter. Cladoxylopsids disappear soon after hypothesized one reason they disappear: is just that- system is too complex hypothesis. Carboniferous forests- ancient fern forests dominated vast wetlands covering most of.