After felling, beech wood may form thyloses, blocking the xylem vessels, so that they can not be sufficiently impregnated with creosote. This decreases the durability and value of the wood for such purposes as railway sleepers. Ebes found that thyloses may be formed throughout the year through pits from wood ray cells next to the xylem vessels. Trials with small logs showed that thyloses appeared sooner at higher temperatures. After a loss of 40-45 % moisture no more thyloses appeared. Fresh uptake of moisture induced further thyloses, unless moisture dropped below about 60 %. Ebes confirmed Klein's observation (1923) that when water was pressed through a branch and air through one of its laterals, the branch developed no thyloses, while the lateral formed many. From this it was concluded that the penetration of air into the vessels caused formation of the thyloses.
To limit thyloses trees should be felled in a season with low temperatures, and drying of the timber should be encouraged by sawing the wood early. More experiments were needed to find how quickly railway sleepers dried.