because of the tension the water molecules in the xylem tissue are under, any break in the column of liquid will cause the column to break. when this happens, that vessel or tracheid will usually be unable to transport any more water. Fourtunately, connections exist between adjoining tracheids and vessels. these are the opening or perforations in the otherwise lignified walls. In this way, the overall flow of the liquid in the xylem will continue unimpeded,