NON-RANDOM VESSEL DISTRIBUTION
One of the fascinating things about wood anatomy is that vessels are rarely randomly distributed in wood. So various types of vessel distribution must be serving some purposes. With the crowded large vessels of earlywood, there is obviously a benefit in providing more conductive tissue early in a growth ring. Coordinately with this, the mechanically strong "fibrous" cells (usually libriform fibers) can be added later in the growth ring, along with narrower, fewer, and more widely-spaced vessel elements. That's just one example of how shifting production of vessels and other associated cell types is a strategy that can benefit woods. Conifers, which have only one type of conductive cells, the tracheid (except for Gnetales, which we must now include in conifers), don't have such options. In the bigger picture, the capability of strategically position vessels (and thereby other cells, too) in wood makes for a wonderful evolutionary strategy for angiosperm woods, and may help explain why angiosperms have been so successful.
Collecting Families into Orders—New Wood Evolution Patterns
In 2010, I published an account of wood of Caryophyllales, not so much as a way of gathering together information, but as a way of showing what we know about wood evolution now that we have molecular-based phylogenetic trees of angiosperm families and orders. In pre-molecular days, information on wood anatomy was collected familky by family, and the hope was that the outlines of a natural system of woody plants would become evident. The title of Solereder's 1885 thesis ("Über die systematische Wert...." –literally, "on the systematic value") denotes a program followed down to the present. But with the 1993 Chase et al. global molecular phylogeny of angiosperms, and its refinements since, the tables have been turned. With molecular phylogenies, we have probable phylogeny of taxonomic units with a high degree of certainty, so those molecular phylogenies and the placement of families within them now tell us how wood has evolved.