In a branch cut from a rapidly transporting plant water snaps away from the cut end .what is the reason?

Due to transpiration pull, the water column found in xylem elements is virtually pulled upwards and outwards from one end, but the same water column is also subjected to another opposing force called gravitational pull. Because of this the water column becomes narrow because of tension. As the outer region of the water column is still adhered strongly to the hydrophilic xylem wall materials the xylem cells are also subjected to tension, hence they become narrow.
Whether or not, the water columns are subjected to such tensions under rapid transpiration conditions can be demonstrated by cutting the twig. When such stems are cut, the water snaps back at the cut ends which clearly indicate that the water columns in plants under favorable transpiring conditions exist in a state of tension.