A primitive Silurian land plant with xylem and phloem but no differentiation in root , stem or leaf , was much-branched Psilophyton . This plant reproducied by spores and respired through stomata on every surface , and probably photosynthesizing in every tissue exposed to light . A primitive Silurian land plant with xylem and phloem but no differentiation in root , stem or leaf , was much-branched Psilophyton , reproducing by spores and breathing through stomata on every surface , and probably photosynthesizing in every tissue exposed to light .