Fig. 15.3-16a and b. Transverse section of wood with banded paratracheal parenchyma. In both species, the parenchyma forms a sheath around the vessels, and the sheath of one vessel is confluent with (touches) the sheath of other vessels. In the upper micrograph (ash, Fraxinus), the parenchyma is rather sparse, with just a narrow band connecting the paratracheal parenchyma around the various vessels. But despite being narrow, the parenchyma cells form a bridge through which water can diffuse relatively freely.

   In the lower micrograph (foxglove tree, Paulownia tomentosa), the parenchyma is abundant, forming a relatively massive water-rich tissue around the vessels. Although the micrograph of foxglove tree appears to have two separate masses of parenchyma, it might be that deeper down in the wood, the two masses of parenchyma are confluent with each other.