What are needles? Green witnesses of the multi-million history of the planet

2024 Author: Henry Conors | [email protected]. Last modified: 2024-02-12 02:45

Inhabitants of the middle lane do not need to explain and tell what the needles on the trees are. Everyone knows that these are the leaves of spruce, pine, larch. They know that even in winter, pines and spruces do not shed their leaves, so they are called evergreens.

The world around us: what are needles in the history of the planet's development

Already in the Paleozoic era (almost 300 million years ago) huge forests of coniferous vegetation (initial forms) covered the planet. Then the reproduction of these forms of vegetation occurred from seeds lying directly on the leaves (hence the assignment of conifers to the category of gymnosperms).

The beginning of the Jurassic period (220 million years ago) after global changes in the planetary climate made it possible for conifers to show their beauty and rare adaptability to a temperate climate.

In recent times (from Jurassic to modern) conifers have lost their privilege but still dominate some temperate zones. Thus, in the territory of the former USSR, forest tracts consisted of almost seventy-five percent of coniferous forests (approximately fiftypercent of them are larch, twenty-one percent are pine (scotch and cedar), and only about two are shade-tolerant conifers (fir and spruce).

What are needles?

Leaf-like (leaf-like) organs of coniferous plants are well adapted to annual changes in the environment - to temperature fluctuations (hot in summer, frosty in winter), to changes in the amount of moisture (excess in spring-summer-autumn, lack of). What are the needles of pines, firs, fir, pseudo-hemlock? These are tough, fairly small (compared to angiosperm leaves) tree needles with a small evaporating surface, but in which, nevertheless, photosynthesis reactions still take place.

Such a familiar spruce

Tetrahedral spruce needles grow singly, spreading throughout the entire tree branch. They are very resilient with not very noticeable (even to the touch) edges, but each tip is even sharper - a small prickly needle with a sharp-sharp tip.

What are the needles of fir trees in a section (section)? This is the wrong rhombus. The lower corner (pointing down) is the largest, it contains the middle vein (needles are a modified leaflet). This design feature makes it possible for the needles to be rigid (prickly and durable). And an additional two layers of cells immediately under the epidermis (outer layer) make the spruce needles even more durable. The length of needles in different types of spruce can be from one to one and a half centimeters.

Each needle is covered with a thick layer of wax coating - this is the cuticle. Have firs layerthe cuticle is the largest, and the higher the air pollution in urban conditions (an unfavorable factor for these plants), the thicker the wax coating, it is in it that exhaust gases dissolve. Spruce saves itself in this way, but lives in urban conditions much less than in natural conditions - the cuticle disintegrates, the needles fall off.

Pine needles

This plant belongs to the largest group of evergreen conifers. Its long leaves of the first year grow like a spruce - one at a time. The second year is interesting because new shoots (twigs-needles) come out of each sinus of the previous year, there can be from two to five (this is inherent in different species). Pine needles fall along with twigs.

Scotch pine - the most common in Europe and Asia - two-needle. The Banks pine (also found in Europe and Asia) has short needles, slightly larger than those of spruce (from two to four centimeters), and just as hard. North American swamp pine is distinguished by the length of its needles - its soft needles grow up to forty-five centimeters.

The American continent is the birthplace of three-coniferous pines.

Five-conifers grow both in Europe and in America. Weymouth pine is the most exotic species among them. Long soft needles are preserved in this plant only on fifteen centimeters of the tips of drooping branches. Crows are very fond of these needles in winter, they peck them as a vitamin supplement.

Our Siberian and Far Eastern cedar is a five-needle pine. The length of the needles does not exceedfive centimeters.

Larch

The needles of this plant fly around every autumn in September-October. It is soft, flat, grows in bunches of short shoots that remain on the tree for a long time, in winter they look like tubercles-warts. Leaf fall helps the needles survive in conditions of extreme gas pollution - all the toxins accumulated by the plant over the summer leave the tree along with the yellowed needles.

Spring brings the tree to life, and in May the larch dresses itself up with tiny emerald green needles. By the end of spring, they grow to two to three centimeters.