The significance of phloem hydrodynamics to plant mortality and survival, which impacts ecosystem-scale carbon and water cycling, is not in dispute. The phloem provides the conduits for products of photosynthesis to be transported to different parts of the plant for consumption or storage. The Munch pressure flow hypothesis (PFH) is the leading framework to mathematically represent this transport. It assumes that osmosis provides the necessary pressure differences to drive water and sucrose within the phloem. Mathematical models utilizing the PFH approximate the phloem by a relatively rigid slender semi-permeable tube. However, the phloem consists of living cells that contract and expand in response to pressure fluctuations. The effect of membrane elasticity on osmotically driven sucrose front speed has rarely been considered and frames the scope here. Laboratory experiments were conducted to elucidate the elastic-to-plastic pressure-deformation relation in membranes and their effect on sucrose front speeds. It is demonstrated that membrane elasticity acts to retard the sucrose front speed. The retardation emerges because of two effects: (a) part of the osmotic pressure is diverted to perform mechanical work to expand the membrane instead of pressurizing water, and (b) expansion of the membrane reduces the sucrose concentration driving osmotic potential due to volume increases and concomitant dilution effects. These results offer a novel perspective about the much discussed presence of sieve plates throughout the phloem acting as structural expansion dampers.Plain Language Summary Plants utilize two interconnected hydraulic systems, the xylem and the phloem, to transport water and sucrose. The xylem provides the necessary pathway for water molecules, extracted from the soil and released back to the atmosphere during photosynthesis, to be transported to the leaf. The phloem moves photosynthates, mainly sucrose, from the leaf to different parts of the plant using the osmotic potential of sucrose along the pathway. The importance of phloem hydrodynamics to plant mortality and survival, which impacts the ecosystem-scale carbon and water cycling, is not in dispute. While the xylem consists of dead cells and is rigid, the phloem consists of living cells and is elastic. The work presented here revisits osmotically driven flows in elastic tubes to focus on the influence of phloem elasticity on flow efficiency using laboratory experiments on idealized elastic semi-permeable membranes. Experimental results are combined with mathematical modeling to show a decrease in transport efficiency because of losses in the osmotic potential necessary to drive the flow. These results offer a new perspective about phloem resilience and the role of sieve plates that connect the sieve elements of the phloem.< Réduire