Stems of cut rose flowers (Rosa hybridaL. cv. ‘Sonia’) were placed in water to study the development of a population of micro‐organisms at the cut surface and in the xylem vessels. The cut surface became covered with bacteria within 2 d of vase life. The bacteria were accompanied by an amorphous substance which was apparently bacterial slime. After 7 d of vase life many fungal hyphae were also found at the cut surface. Inside the xylem vessels the bacteria were often clustered at the inter‐vessel pits. After 4 d of vase life most of the vessels that had been opened by cutting contained bacteria. Only a few xylem elements, located several centimeters from the cut surface, contained an amorphous substance. A few fungal hyphae were observed inside the xylem vessels. No yeasts were found, either at the cut surface or inside the xylem.Pseudomonasspecies accounted for more than 70% of the total bacterial population of the cut surface and the xylem vessels, andEnterobacterspecies (mainlyEnt. agglomerans) for less than 10%.Acinetobacter, Aeromonas, Alcaligenes, Bacillus, CitrobacterandFlavobacteriumwere occasionally o