Xylem cells are elongated cells with lignified secondary thickening of the cell walls. Xylem cells are specialised for conduction of water, and first appeared in plants during their transition to land in the Silurian period more than 425 million years ago (see Cooksonia). The possession of xylem defines the vascular plants or Tracheophytes.
hobo. a hobo is an itinerant worker, a career which sprang up during the depression. A hobo, unlike a bum or a tramp, is more than willing to work, but mostly for a short duration, as their main impetus is travel, the love of the journey above the actual destination.
Define holism. holism synonyms, holism pronunciation, holism translation, English dictionary definition of holism. n. 1. The theory that living matter or reality is made up of organic or unified wholes that are greater than the simple sum of their parts. 2.