Versatile and Beautiful
Have you ever noticed how beautiful objects are which are made of wood? The people of Bible times also appreciated and used beautiful wood. The ancient Phoenicians (Canaanites) exported cedar wood for temples and palaces of many contemporary empires. One of their more famous customers was the Assyrian Sennacherib (about 700 B.C.) who commissioned two fleets of ships to be built from the cedars of Lebanon, one for the Tigris River and the other on the Euphrates River. King David himself made extensive use of cedar wood in his palace and his son, Solomon, proved to be even more enthusiastic about the cedars of Lebanon (Cedrus labani). Solomon promised massive payments to his friend and father-in-law King Hiram of Tyre in return for importing cedar trees for the temple. Much later, the Romans sought cedar wood from Lebanon for their own ships. However, Emperor Hadrian cautioned against over-exploiting this resource. Unfortunately, nobody listened and few of these trees remain today.
The cedars of Lebanon trees exhibit a wide flat canopy and they can attain a height of 80-120 feet (24-37 m) with trunks of 4-8 ft (1.2-2.4 m) in diameter. Under ideal conditions, the trees can live for 1000 years. Their wood is fragrant, beautiful and remarkably durable. King Solomon also purchased other kinds of wood for his temple and palace. In I Kings 6 we read how the cherubim over the ark of the covenant in the temple were carved from olive wood (Olea europaea) which is hard, rich in colour, with straight grain and fine texture. However, it is not suitable for outdoor construction. Another beautiful wood product that King Hiram brought to Solomon (probably from India) was red sandal-wood (Pterocarpus santalinus), referred to in I Kings 10:12 as almug wood. This wood is also dense, hard, close-grained and of a fine red colour. King Solomon used it for supports for his palace and temple as well as for fine musical instruments like the harp and the lyre.
Wood Comes from Trees
Perhaps we do not reflect enough on what an amazing material wood is. We all know what wood looks like, but we seldom think about how it develops. Indeed, there are lots of plants with conducting (vascular) tissue whose stems never grow any thicker and thus which have no wood. They may contain one or more strands of phloem and xylem (vascular) tissue running from root tip to stem tip. The phloem transports products of photosynthesis down through living cells to all parts of the plant. The xylem, on the other hand, consists of empty cells with thickened walls made of indigestible cellulose and lignin. Arranged end to end, these xylem cells transport water from the roots to all parts of the plant. Specimens with no secondary thickening are called herbaceous plants and typically last less than a year.
A plant needs special innovations if it is to develop secondary thickening or secondary xylem (wood). Like stem cells in our bodies which are able to continue dividing indefinitely, many plants possess a tissue with cells that are able to divide indefinitely. This is called the cambium. The cambium produces new cells on its inner circumference that develop into rings of wood. On the outer circumference, the cambium produces phloem cells just under the bark. As the cambium continues to divide, the tree trunk becomes thicker with more and more wood.
Fossil Wood in Unexpected Places
The vast majority of plant species are not woody. We possibly do not notice that trees are in the minority of plant kinds since they are so conspicuous. From an evolutionary point of view, biologists long assumed that small non-woody plants developed long before plants with the capacity to form wood appeared. They looked in the fossil record and found a lot of non-woody plants in the lowest levels of Devonian rock. They therefore figured that woody thickening of plant stems is a sophisticated feature that followed the appearance of many herbaceous land plants. This belief was challenged however by the discovery of a woody artifact in lowest level Devonian rocks in the Campbellton Formation of New Brunswick. This find and a similar one from France were found at the same level as the lowest lying vascular plant fossils.1 How, if evolution had indeed occurred, could the descendant appear at the same time as the supposed ancestor?
More recently another woody plant fossil has been found in lowest lying Devonian rock on the Gaspe Peninsula of Quebec, not far from the Campbellton Formation in northern New Brunswick. Making the best of a bad situation, the authors of this last Canadian study conclude that the capacity to make wood appeared in plants even before many vascular plants had actually developed.2 It is certainly safe to say that botanists have no reasonable evolutionary explanation for how the capacity to make wood appeared. However, we have recently learned that at the molecular level, the formation of wood is a spectacular process!
Molecular Machines Produce Unique Features
A study just published (January 2021) from Europe has managed to observe the development of xylem cells before they become empty water conducting vessels. Apparently before they die, these cells organize the depositing of bands and spirals made of cellulose to strengthen the cell wall against collapse when the cell is empty. This study reports that the cell needs the help of special proteins in order to produce the amazing pattern of thickening so characteristic of each type of wood. According to this study microtubules which are actually part of the cell’s cytoskeleton, here provide tracks under the cell’s outer membrane. Nobody knows how the microfibrils choose the unique filigree patterns that guide the deposition machinery (molecular machines in the plasma membrane). “This machinery moves along the microtubules like an asphalt paver and continuously deposits wall material on the outside of the cells. The microtubules thus act like an instruction manual for cell wall synthesis.” 3 This elaborate process results in extremely strong walls that make the water conducting wood so efficient.
The capacity to form wood is totally amazing! I am not sure if the ancient peoples gave thanks for that blessing, but there is no doubt that we should be thankful for the creation of plants, including all those wonderful trees!
- Philippe Gerrienne et al. A simple type of wood in two early Devonian plants. Science 333: 837 and Supporting Online Material Text pp. 6. See SOM Text p. 1.
- Laurel A. Hoffman and Alexandru M. F. Tomescu. 2013. An early origin of secondary growth Franheuberia gerriennei gen. nov. et sp. nov. from the Lower Devonian of Gaspe (Quebec, Canada). American Journal of Botany. 100 (4): 754-763. See p. 761.
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