In the parks and gardens of many cities, an aesthetic and very particular practice is carried out with plane trees ( Platanus × hispanica ). During the winter, and after pruning, some young branches are left uncut, and two of them, from different trees, are intertwined with each other . They are then fastened, with strings or ribbons, and left throughout the year.
The following year the rope is changed, so that it does not cause damage to the trees, and it is repeated, until, a few years later, they can be untied: both branches are already joined. Several years later, when the branches have thickened enough, both have grown intertwined in such a way that they are perfectly fused, as if it were just a branch that comes out of one trunk and ends in another, forming arches that are highly appreciated by the public. because when filled with leaves, they provide a magnificent shade.
With this simple technique, a skilled gardener can achieve true works of art by intertwining different branches and forming spectacular structures. However, they are events that can also be found in nature.
inoculation
How these branches come to merge has its answer in a biological process that occurs in plants, called inosculation . Process that facilitates not only this branch fusion technique, but also others such as grafting.
Inosculation begins when two branches come into contact with each other. Generally, it happens on young branches, although it can also happen with older branches, and even directly with the stem, as long as enough time passes. Simple contact is not enough for bonding to occur; in the natural process the wind has a significant effect; by causing one plant to rub against the other, the bark of one has an abrasive effect on the other , and vice versa.
As they wear away, the cambium , the tissue under the bark, becomes exposed. This tissue is made up of a layer of embryonic cells that are responsible for making the branch or trunk grow in width, generally forming a new ring each year in its growth.
When the cambium of two different branches comes into contact, the embryonic cell layer may eventually fuse, forming a single continuous layer that encompasses both branches. And since that happens, any subsequent growth will form a new ring of log that will hug the two branches. From that moment, they become a single branch, sharing the newer and outer vascular bundles. Even if it were cut, the two original branches would still be appreciated inside.
In the natural state it is relatively rare for two young branches to remain in contact long enough for the cambium of both to fuse, and generally this inoculation process is more common on firm stems, which move much less. On the other hand, in this case the crust is much thicker, so getting it to wear down enough takes a long time. When gardeners intertwine two branches of two shade plane trees, they are forcing the union to take place, and as one branch is in permanent contact with the other, inosculation ends up taking place, if only by mere growth across the width of the leaves. branches.
Can other trees be inoculated?
In general, plants have much more tolerance and plasticity to this type of process, so it is not uncommon to find many species among which an inoculation of branches or stems can be achieved. Many of the trees of the Rosaceae family, such as the apple tree, the peach tree, the pear tree, the plum tree or the almond tree, are relatively easy to inoculate. It can also be found in poplar, hazel, beech, chestnut, dogwood, elm, maple, ficus, willow or laburnum trees.
The grafting technique , as mentioned, follows the same principle. In this case, a branch of a tree is cut and its edge is sharpened, and inserted into a slanting wound made on the trunk or branch of another tree. After one or two years of care, with the area well secured to promote inosculation, the new branch will behave normally, as if it were a branch that was always there. This technique is not only used to obtain garden plants with strong root systems, typical of wild plants —as in the case of the rosebush—, but also to ensure that certain trees grow effectively in inhospitable places, by being grafted on root systems of other trees adapted to that climate.
Some gardeners even manage to have a single plant that produces different types of fruit on different branches , like an apple tree that produces different varieties of apple, or a vine divided into two halves, that produces a different type of grape in each half.
Inoculation between species
Generally, these processes occur in two plants of the same species. But in some cases it is possible to successfully graft plants of different species . An orange tree that has a lemon branch, or a quince with a part of the plant that produces apples are curious examples that, although they require a mixture of experience and luck, it is possible to obtain them.
And it can also occur in the wild. It usually happens when two trees grow very close, one next to the other, and there comes a time when their thickness makes them come into contact, although there may be other causes. A fascinating inoculation between two trunks of two different species, which happened a long time ago, can be seen in the Gijón Botanical Garden . There, it is believed, strong winds partially knocked down one of the trees, which was left leaning on the other. Still alive, both continued to grow, one leaning on the other, and as if they were two intertwined banana branches, they ended up merging in an inseparable mutual embrace.
References:
Lievestro, T. 2020. Living Trees as Structural Elements for Vertical Forest Engineering.
Ludwig, F. et al. 2019. Living bridges using aerial roots of ficus elastica – an interdisciplinary perspective. Scientific Reports, 9(1), 12226. DOI: 10.1038/s41598-019-48652-w
Pérez Morales, C. 1999. Morphology of spermatophytes. Ed. Celarayn.
Vallas, T. et al. 2017. Using nature in architecture: Building a living house with mycelium and trees. Frontiers of Architectural Research, 6(3), 318-328. DOI: 10.1016/j.foar.2017.05.003
