Oomycetes and fungi grow in a polarized manner through the process of tip growth. This is a complex process, involving extension at the apex of the cell and the movement of the cytoplasm forward, as the tip extends. The mechanisms that underlie this growth are not clearly understood, but it is thought that the process is driven by the tip yielding to turgor pressure. Mass flow, the process where bulk flow of material occurs down a pressure gradient, may play a role in tip growth moving the cytoplasm forward. This has previously been demonstrated in mycelia of the oomycete Achlya bisexualis and in single hypha of the fungus Neurospora crassa. Microinjected silicone oil droplets were observed to move in the predicted direction after the establishment of an imposed pressure gradient. In order to test for mass flow in a single hypha of A. bisexualis the work in this thesis describes the microinjection of silicone oil droplets into hyphae. Pressure gradients were imposed by the addition of hyperosmotic and hypoosmotic solutions to the hyphae. In majority of experiments, after both hypo- and hyperosmotic treatments, the oil droplets moved down the imposed gradient in the predicted direction. This supports the existence of mass flow in single hypha of A. bisexualis. The Hagen-Poiseuille equation was used to calculate the theoretical rate of mass flow occurring within the hypha and this was compared to observed rates. To create a more streamlined system for future study, this thesis also describes Lab-on-a-Chip technology and the design of chips, which isolate single hyphae from the rest of the mycelium. While microinjection of oil was unsuccessful on these chips in the present study, with modification in the future this new system may produce a more controlled environment for the study of mass flow.