Phloem is the vascular tissue that moves the products of photosynthesis. Living sieve-tube cells, supported by companion cells, carry a sugar-rich sap (mostly sucrose) from "sources" such as mature leaves to "sinks" such as roots, new shoots and developing flowers. Flow runs whichever way supply and demand dictate, so phloem moves material both up and down.
In practice
Phloem is the reason nutrients are called mobile or immobile. Nitrogen, phosphorus, potassium and magnesium move readily in phloem, so a plant short of them strips old leaves to feed new growth, and deficiency shows low on the plant first. Calcium, boron and largely iron are poorly phloem-mobile, so their shortages show on new growth.
In late flower, buds are the main sink. Leaf senescence and nutrient remobilisation into flowers run through phloem, which is the biology behind both the natural fade and the GenetixBay nitrogen taper.
Sap-sucking pests such as aphids and whiteflies feed directly on phloem sap; their honeydew is excess sugar.
Don't confuse with
- Xylem: moves water and ions up from roots.
- Bark: outer tissue that, on woody plants, contains phloem.
- Resin: made in trichomes, not carried in phloem.
The process in chloroplasts that uses light energy to turn carbon dioxide and water into sugars and oxygen; cannabis uses the C3 pathway.A nutrient deficiency is a shortage of an essential element in the plant tissue, causing characteristic symptoms; the cause is often pH or uptake rather than an empty feed.The programmed ageing and breakdown of leaves and other tissues, in which the plant recycles nutrients (especially nitrogen) from old leaves to developing flowers and seeds.Gradually cutting nitrogen in late flower, toward zero near the finish, while still feeding phosphorus, potassium, calcium, magnesium, sulfur and micronutrients; GenetixBay's alternative to flushing.Small soft-bodied sap-sucking insects of the family Aphididae that cluster on stems and leaf undersides, excrete sticky honeydew and multiply rapidly by live birth.Small white-winged sap-sucking insects of the family Aleyrodidae, mainly Trialeurodes vaporariorum and Bemisia tabaci, that fly up when disturbed and coat leaves in honeydew.The plant's water-conducting tissue, which carries water and dissolved mineral ions upward from roots to leaves, driven mainly by transpiration.A hair-like outgrowth of the plant's skin; in cannabis the glandular types make and store the resin holding cannabinoids and terpenes.
