Fig. 15.3-14. Transverse section of Robinia pseudoacacia (black locust or false acacia). Most of the vessels here are plugged with tyloses. They had cavitated at some point, and subsequently the adjacent paratracheal parenchyma cells sealed them with tyloses. This plugging is not confined to just this level of the vessels; if a longitudinal section were available, almost all the length of the vessel would be seen to be plugged.