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.
From Wikipedia, the free encyclopedia. Hypertrophic Osteodystrophy (HOD) is a bone disease that occurs in fast-growing large and giant breed dogs. The disorder is sometimes referred to as metaphyseal osteopathy, and typically first presents between the ages of 2 and 7 months.OD is characterized by decreased blood flow to the metaphysis (the part of the bone adjacent to the joint) leading to a failure of ossification (bone formation) and necrosis and inflammation of cancellous bone.