To survive, the plants are obliged of préléver water in their medium.

The plants, for the majority, draw from the ground l’eau and rock salt which are necessary for them. The hairs absorbents of the young roots play for that an essential part.

The mineral elements penetrate with l’état d’ions, either starting from the solution of the ground, qu’ils free or are inserted in organic complexes (chélats), or starting from colloids on which they are adsorbed. L’absorption is sensitive to many factors, which hold, the ones with absorbing l’organism, the others with l’environnement.

Physiological L’importance of l’état of fabrics, l’influence of the temperature and l’aeration bring to call upon beside the physical causes of l’absorption the setting concerned of metabolic processes.

The mechanisms are primarily the same ones as in intercellular transport: for water, osmosis; for the ions, passive diffusion and membrane enzymatic pumps d’influx or d’efflux.

At the terrestrial plants, l’absorption of l’eau and mineral elements s’effectue primarily by the hairs absorbents (fig. 1), cells giant, very lengthened, located close to l’extremity of the roots. Their density is considerable (jusqu’à 2 500 per cm2 at the graminaceous ones); their number can reach, for a plant of average importance, several billion. On the whole for a foot deseigle one could evaluate (Dittmer) the total length of the roots at 250 km and their surface absorbing to 470 m2 .

The hairs absorbents are rare at the trees (oak, beech), and even absent at much of conifers (pine); they are then replaced by a mushroom felting symbions (mycorhizes). Watery plants (Elodea) n’ont not of hairs absorbents, except if they are in l’obscurity; l’absorption s’effectue simply by the not subérifiées parts of the root. The algae absorb by all their surface.

The absorbing hair does not appear to have absorbing virtues particular. They are only its morphological characteristics: considerable surface (which multiplies by one facteurallant from 2 to 10 that of the roots), thin membrane, large vacuole, which explains its role. The volume of the ground explored by the plant is still increased owing to the fact that the solution of the ground forms a network of flow lines having a certain cohesion.

A plant is able d’attirer l’eau ground and the dissolved salts located at several centimetres or even several decimetres of him. Atmospheric L’eau, fog or dew, can be absorbed by the aerial roots or those which run to short-nap cloth of the ground. It is thus in the deserts, where the night dew is particularly abundant.

Sometimes a special conformation facilitates this capture: for example, at the orchises épiphytes, the periphery of the roots is occupied by a formed veil of several bases of round and not very jointed cells. The sheets also contribute to l’absorption of l’eau under the natural conditions.

Absorptive once, water goes up inside the plant. They pass in the interstices between 2 cells. Once arrived in top of the plant, water evaporates.