In most of the gymnosperms, like conifers and cycads, vessels are absent and the wood is made entirely of tracheids. Such wood is known as nonporous.
In angiosperms, on the other hand, the wood consists of both tracheids and vessels. The wide vessels appear as pores between otherwise small sized tracheary elements. Such a wood is known as porous. In porous wood, if vessels have essentially equal diameters and are uniformly distributed throughout the ring, the wood is known as diffuse porous. It is characteristic of plants growing in tropics.