Water is drawn upward from the roots through plant tissue to the leaves by what?

The process of transpiration draws water from the roots to the leaves.

Transpiration is the process by which moisture  is drawn or carried from the roots up to the small pores on the underside  leaves of the plant. The water changes to vapor and is released to the atmosphere through these pores called stomata.

As water evaporates through the stomata in the leaves, a negative pressure  (also  called tension or suction) is created in the leaves and tissues of the xylem. The negative pressure exerts a pulling  force that draws water up to the leaves from the roots.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.