Plant Physiology Archive

ROOT PRESSURE

If the stem of a young seedling is cut off just above the soil, the stump will often exude sap from the cut xylem for many hours. If a manometer is sealed over the stump, positive pressures can be measured. …

Diffusion

The net movement of molecules from region of high concentration to regions of low concentration that is, down the concentration gradient. Water molecules in a solution are not static they are in continuous motion, colliding with one another and exchanging …

WATER IN THE SOIL

The water content and the rate of water movement in soils depend to a large extent on soil type and soil structure. At one extreme is sand, in which the soil particles may be 1 mm or more in diameter. …

WATER IN PLANT LIFE

Water makes up most of the mass of plant cells. Each cell contains a large water-filled vacuole. In such cells the cytoplasm makes up only 5 to 10% of the cell volume; the remainder is vacuole. Water typically constitutes 80 …

Sources and Sinks

Sources include any exporting organs, typically mature leaves, that are capable of producing photosynthate in excess of their own needs. The term photosynthate refers to products of photosynthesis. Another type of source is a storage organ during the exporting phase …

PATHWAYS OF TRANSLOCATION

The two long-distance transport pathways—the phloem and the xylem—extend throughout the plant body. The phloem is generally found on the outer side of both primary and secondary vascular tissues. In plants with secondary growth the phloem constitutes the inner bark. The …