The branches of Ginkgo are tall and straight. The bark is shallowly cracked and light gray when young. As the tree ages, the cracks and color gradually become darker. There are obvious differences in crack shape and length between strains. From strips to crosses, lengths vary from 40 cm to 100 cm.
The height of the real ginkgo tree can exceed 30 meters, and the diameter at breast height exceeds 3 meters. Under suitable conditions, ginkgo can grow into a tree with a straight, round trunk and low sharpness, making it a high-quality timber. A suitable ecological environment is the basis for ensuring that ginkgo trees grow into high-quality materials with low sharpness. The Ginkgo biloba on Xitianmu Mountain in Lin'an County, Zhejiang Province, one of the starting places, is accompanied by tall golden pine and other forest trees. In addition, the humus soil in the mountain is loose and fertile. Therefore, the plants grow more vigorously and the trunks are straight. From the ground, at least There is a tree trunk more than ten meters long, almost as thick as the top and bottom. An adult tree born in 1990 has a height of 23-26 meters, a single tree volume of about 1 cubic meter, and is still at its peak growth period.
For ginkgo trees that are in an isolated state, as well as ginkgo trees that are distributed in the north (such as Liaoning) or south (such as Guangdong), the height of the branches on the main trunk is generally less than 2 meters, and the thickness of the upper and lower parts of the main trunk is very different, especially in The difference between the upper and lower branches of the branch is more prominent. This is due to plant growth being inhibited by various factors. The backbone branches that are close to whorls sometimes greatly inhibit the growth of the main trunk. Although this situation is extremely detrimental to the production of high-quality wood, it is conducive to the flowering and fruiting of the plant.
The xylem of Ginkgo biloba is composed of round tracheids with edged holes. There are large calcium oxalate crystals in some parenchyma cells, with a red appearance, extremely underdeveloped rays, and obvious growth rings. The cortex of Ginkgo is thicker, with small rhombus or oval lenticels. The outer skin is generally cracked in strips or small pieces, with slight interdigitation to varying degrees.
There are a large number of hidden buds on the main trunk of Ginkgo biloba. Short branches sprouted from these latent buds can sometimes bloom and bear fruit. Under certain conditions, these stable buds will develop and expand, forming rows of tumor-like protrusions. At the base of the main branch or the bend of the big branch, this protrusion is stalactite-shaped, commonly known as "breast", "silver milk" or "tree milk". The largest tree milk length that has been seen exceeds 2.0 meters, and the base diameter is greater than 28 centimeters (Guizhou). At the base of the trunk, this protrusion expands laterally to form a knob, which the masses call a "chair." Sometimes you can see rows of horizontally arranged wart-like protrusions on the main trunk, which are also developed from the adventitious buds of Ginkgo biloba. Unlike tree milk, it has no obvious geotropism. The mechanism that produces this bulge is not yet clear, but preliminary inferences may be related to the inhibition of plant growth.
Both male and female Ginkgo plants produce tree milk, but the proportion of female plants producing tree milk is significantly higher than that of male plants. Therefore, there is a saying among the masses that "Ginkgo can only be strong if it grows tree milk and chairs."
In fact, not only big trees can grow tree milk, but even seedlings that are one or two years old, or even sprouts that have just been sown for two months, will suffer from the growth of the roots below the stem when the root growth is blocked or under other specific conditions. , can also grow small nodules; on the contrary, not every adult ginkgo that has entered the fruiting stage can grow tree milk. Therefore, there is no basis for taking the formation of tree milk as a sign of entering the fruiting stage. It is also worth doing some in-depth research on whether the difficulty of producing tree milk can be used to early identify the fruiting and other characteristics of ginkgo. There is currently a lack of unified understanding of the formation of tree milk. Some people think it is a physiological phenomenon and point out that this is a primitive trait that is unique to remnant species that originated early. Some people think that the formation of tree milk may be related to the thickness of the bark. If the periderm is thin, it is easy to produce tree milk. Some people think that this is a pathological phenomenon, and the ginkgo tissue is stimulated by some external factors to grow tumors. However, they have not confirmed what microorganisms are responsible for the formation of tree milk.
The growth of tree milk has obvious geotropism. It roots quickly as soon as it touches the ground. The isolated tree milk can grow roots in less than a month when cultivated under suitable conditions. These facts tell us that tree milk is an aerial root. This view is further confirmed by the fact that large quantities of tree milk can be induced when the roots of ginkgo trees are greatly cut and their root growth is inhibited.
When dissecting the newly formed tree milk, we can see several circles of circular cavities arranged along the bark layer of the tree. The cavity is filled with purple sap, and its structure is similar to that of the radicle tissue. Nutritional analysis of tree milk tissue revealed that it contains a large amount of starch. All this shows that it is more reasonable to judge it as an aerial root tissue.
The tree milk that grows on the trunk of adult branches is often at the corners of drooping branches. Water droplets often accumulate in these parts, and organic nutrients transported downwards tend to accumulate in these places. This creates conditions for the formation and growth of adventitious roots from both the inside and outside of the tree. Stunted growth and humid climate further encourage the production of adventitious roots, which is also the root cause of regional differences in the formation of tree milk.
Scientists have determined the content of important organic components in apricot wood. The mannan content is 7.06%, the galactan content is 1.87%, and the methoxyl content of raw wood is 2.41%. Air-drying The methoxyl content of wood is 4.55%, and the methoxyl content of dry wood is 5.20%. The tannin content of Ginkgo bark is 10.0%, and the coloring degree is 1.17.
Among the oxidation products obtained by oxidizing ginkgo sapwood, inner bark and outer bark with nitrobenzene in alkaline medium, vanillin has the highest content, followed by p-hydroxybenzaldehyde and p-hydroxyazobenzene. There are also small amounts of vanillic acid, formyl vanillic acid, syringaldehyde, etc.