Although plant biologists have long been studying how plant xylem (sapwood) transports water from the roots to the leaves, studies as to its use as a filter have been neglected. To explore this uncharted realm, Rohit Karnik and his team from MIT used xylem from conifer wood, which is formed by cells that grow in parallel with closed ends. The water flows through the material through small holes covered in a membrane with nanoscale pores, which filters out impurities. 

To test their filer, the team cut one inch long sections of a white pine branch, peeled the bark , inserted the sapwood into a tube and sealed the gaps with epoxy. In tests, the sapwood filter was able to filter out particles over 100 nanometers, which includes the E. coli bacteria. Although the sapwood filter has some limitations—it cannot filter viruses and the wood must be freshly cut—the discovery could lead to the development of cheap, easy to make filters that could be put into widespread use.