Xylem Quotes

All I want is to cultivate curiosity. Yes, my old friend remains undiminished even now: the simple yearning to know. If these students cannot tell a xylem from a phloem, it will not unduly handicap their college hopes or impede their careers. But their lives will depend entirely on whether they possess wonder, an eye for beauty. For many people, the unknown is something to fear. Instead I want to give my students the humility to believe that anything they do not understand therefore possesses an elegant magic.

As oaks age they typically lose much of their inner xylem tissue, creating large hollow spaces within their trunks that serve as home to countless creatures, from rare fungi to raccoons, opossums, squirrels, bats, bobcats, and even black bears. We have been led to think that once there are hollow spaces created by rot within a tree trunk, that tree must come down. Not so! Such “rot” is normal and does not affect the living cambium that lies just under the bark of your oak nor the functional strength of the trunk. Hollow trunks are just one feature of ancient oaks that makes them such valuable ecological additions to our landscapes. Beating

Lignin is a linkage of three aromatic alcohols—coumaryl, coniferyl, and sinapyl—which fill the spaces in cell walls that are not already occupied by other substances, even ousting water molecules to do so. It thus forms a very strong hydrophobic net, cementing all the cell-wall elements in place and providing strength and rigidity to the xylem. It also provides an important barrier to fungal and bacterial infections. When a tree is invaded by disease, it seals off the infected section with a wall of lignin so that the disease cannot spread. Lignin is so tough that getting rid of it is a costly process in pulp-and-paper plants. The acids needed to break down lignin in pulpwood are the chief pollutants such mills contribute to the environment.

And lifting water is just one of the many jobs that the phloem, xylem, and cambium perform. They also manufacture lignin and cellulose; regulate the storage and production of tannin, sap, gum, oils, and resins; dole out minerals and nutrients; convert starches into sugars for future growth (which is where maple syrup comes into the picture); and goodness knows what else. But because all this is happening in such a thin layer, it also leaves the tree terribly vulnerable to invasive organisms. To combat this, trees have formed elaborate defense mechanisms. The reason a rubber tree seeps latex when cut is that this is its way of saying to insects and other organisms, “Not tasty. Nothing here for you. Go away.” Trees can also deter destructive creatures like caterpillars by flooding their leaves with tannin, which makes the leaves less tasty and so inclines the caterpillars to look elsewhere. When infestations are particularly severe, some trees can even communicate the fact. Some species of oak release a chemical that tells other oaks in the vicinity that an attack is under way. In response, the neighboring oaks step up their tannin production the better to withstand the coming onslaught. By such means, of course, does nature tick along. The problem arises when a tree encounters an attacker for which evolution has left it unprepared, and seldom has a tree been more helpless against an invader than the American chestnut against Endothia parasitica. It enters a chestnut effortlessly, devours the cambium cells, and positions itself for attack on the next tree before the tree has the faintest idea,

All I want is to cultivate curiosity. Yes, my old friend remains undiminished even now: the simple yearning to know. If these students cannot tell a xylem from a phloem, it will not unduly handicap their college hopes or impede their careers. But their lives will depend entirely on whether they possess wonder, an eye for beauty. For many people, the unknown is something to fear. Instead I want to give my students the humility to believe that anything they do not understand therefore possesses an elegant magic.

A tree is a vast thing full of heavy mass. But that mass is mostly inert. The real life of the tree happens in three very thin layers—the phloem, xylem, and cambium. These thin layers are just beneath the bark and they are the envelope of life around the heartwood at the center of the tree.

The burst of life that took centuries to build, revealed in an old tree trunk's cross section. At its center, material memories of the sapling that this tree once was. Year after it grew by accretion, adding successive layers of the interplay of xylem and phloem, water in and water out, sap traveling up and down, transporting complexities under the corky protection of callous bark. If we could read the code of this great being, we would hear tales of drought summers or deep winter snows melting into spring overflow. The history of a life much longer than any human's tells its tale in concentric rings.

The word “moss” is commonly applied to plants which are not actually mosses. Reindeer “moss” is a lichen, Spanish “moss” is a flowering plant, sea “moss” is an alga, and club “moss” is a lycophyte. So what is a moss? A true moss or bryophyte is the most primitive of land plants. Mosses are often described by what they lack, in comparison to the more familiar higher plants. They lack flowers, fruits, and seeds and have no roots. They have no vascular system, no xylem and phloem to conduct water internally. They are the most simple of plants, and in their simplicity, elegant. With just a few rudimentary components of stem and leaf, evolution has produced some 22,000 species of moss worldwide. Each one is a variation on a theme, a unique creation designed for success in tiny niches in virtually every ecosystem.

Oak-inhabiting mistletoes (Phoradendron spp.) are hemiparasites, meaning they are just a little bit parasitic. They photosynthesize 98% of their energy with their own green leaves, but they do sink roots into host branches that penetrate the xylem and suck up some water. Studies on California mistletoe, a hemiparasite on several western oak species, showed that it had no ill effects on its host oaks and acted more like an epiphyte than a parasite (Koenig et al. 2018).

Plants have two kinds of vessels: xylem, which moves water and the minerals dissolved in it from the roots; and phloem, which distributes the products of photosynthesis from leaves to the rest of plant.

The suction of transpirational pull places water under tension in the xylem of an actively transpiring plant. Thus, when stems are cut, air is drawn into the exposed vessels and blocks the flow of water. In the garden, flower stems should always be cut longer than desired, and recut to the correct length while holding the stems under water. If the stems are then quickly transferred to a vase, the transpiration stream continues uninterrupted, without the blossoms wilting. Scissor-type pruning shears or a sharp knife should be used to make clean cuts so the ends of the xylem vessels remain open.