In the “Mikrographie des Holzes der auf Java vorkommenden Baumarten” I described 991 kinds of wood. Several of these belong to large genera, the majority to small. I found remarkably wide variations in the wood-anatomy of several specimens belonging to a single species of a large genus. These intraspecific differences in large genera are generally larger than interspecific differences in small genera. When identifying species by means of wood-anatomical characters, the wide intraspecific variability in large genera obstructs identification whereas in small genera identification is usually relatively easily executed. As a result, it is much easier to compose a key to the species in a small genus than in a large one. In my key to the Javan woods (Anatomische Bestimmungstabelle für die javanischen Hölzer, 1940, 83) it is repeatedly demonstrated; also in Mikrographie passim that taxonomic relationships are often blurred by this peculiar circumstance.