Xylem is vascular tissue made of hollow, dead, lignified cells (vessels and tracheids) that form continuous pipes from roots to leaves. Water moves up under tension created by transpiration at the leaves, carrying nitrate, calcium, potassium and other ions taken up by the roots. Xylem also gives stems much of their strength; wood is mostly xylem.
In practice
Xylem explains several growing problems:
- Calcium and boron travel almost only in the xylem, so they go where water goes. Fast new growth in humid, still air (low transpiration) can show calcium-type symptoms even with plenty in the feed.
- Wilting in hot, dry rooms happens when water loss beats what the roots and xylem can supply.
- Clones: cutting stems underwater or quickly into the rooting medium avoids air entering the xylem (embolism), which can block water flow.
- Wilt pathogens such as Fusarium oxysporum block xylem, causing wilting even in moist media.
Don't confuse with
- Phloem: carries sugars and mobile nutrients, both up and down.
- Pith: soft central tissue of the stem.
- Cambium: the layer that makes new xylem and phloem.
The evaporation of water from a plant, mainly through open stomata, which pulls water and dissolved nutrients up from the roots.Nitrate (NO3-) is the main form of nitrogen in hydroponic and soilless feeds; its uptake tends to push root-zone pH upward.Boron (B) is a micronutrient needed for cell-wall structure and growing tips; the gap between deficient and toxic levels is narrow.A dark, ventilated space where freshly harvested cannabis is dried under controlled temperature, humidity and gentle airflow, usually for 7-14 days.A soil-borne fungal disease, chiefly Fusarium oxysporum, that blocks water-conducting tissue, causing one-sided yellowing, wilting and brown streaks inside the stem.The plant's living transport tissue that carries sugars, amino acids, hormones and mobile nutrients from leaves to roots, buds and other growing parts.A mobile nutrient is one the plant can move from older leaves to new growth, so its deficiency shows first on lower, older leaves: N, P, K, Mg, Cl, Mo.Microscopic pores, mostly on the underside of leaves, each opened and closed by two guard cells to control gas exchange and water loss.A microscopic tube-like outgrowth of a single root epidermal cell near the root tip that greatly increases surface area for water and nutrient uptake.
