● Food, `color{brown}("primarily sucrose,")` is transported by the vascular tissue `color{brown}("phloem")` from a `color{brown}("source to a sink. ")`
● Usually the `color{brown}("source")` is understood to be that part of the plant which `color{brown}("synthesises the food,")` i.e., the leaf, and `color{violet}("sink,")` the part that needs or `color{violet}("stores the food.")`
● But, the `color{violet}("source and sink")` may be`color{brown}(" reversed")` depending on the `color{brown}("season,")` or the plant’s needs.
● Sugar stored in roots may be `color{brown}("mobilised")` to become a `color{violet}("source of food")` in the `color{brown}("early spring")` when the buds of trees, act as sink; they need energy for growth and development of the `color{violet}("photosynthetic apparatus.")`
● Since the `color{brown}("source-sink relationship")` is variable, the direction of movement in the `color{violet}("phloem")` can be upwards or downwards, i.e., `color{brown}("bi-directional.")`
● This contrasts with that of the `color{brown}("xylem")` where the movement is always `color{brown}("unidirectional,")` i.e., upwards.
● Hence, unlike `color{brown}("one-way flow of water")` in `color{violet}("transpiration, food in phloem sap")` can be transported in any required direction so long as there is a source of sugar and a sink able to use, store or remove the sugar.
● `color{violet}("Phloem sap")` is mainly `color{brown}("water and sucrose,")` but other `color{brown}("sugars, hormones")` and `color{brown}("amino acids")` are also transported or `color{brown}("translocated")` through `color{violet}("phloem.")`
● Food, `color{brown}("primarily sucrose,")` is transported by the vascular tissue `color{brown}("phloem")` from a `color{brown}("source to a sink. ")`
● Usually the `color{brown}("source")` is understood to be that part of the plant which `color{brown}("synthesises the food,")` i.e., the leaf, and `color{violet}("sink,")` the part that needs or `color{violet}("stores the food.")`
● But, the `color{violet}("source and sink")` may be`color{brown}(" reversed")` depending on the `color{brown}("season,")` or the plant’s needs.
● Sugar stored in roots may be `color{brown}("mobilised")` to become a `color{violet}("source of food")` in the `color{brown}("early spring")` when the buds of trees, act as sink; they need energy for growth and development of the `color{violet}("photosynthetic apparatus.")`
● Since the `color{brown}("source-sink relationship")` is variable, the direction of movement in the `color{violet}("phloem")` can be upwards or downwards, i.e., `color{brown}("bi-directional.")`
● This contrasts with that of the `color{brown}("xylem")` where the movement is always `color{brown}("unidirectional,")` i.e., upwards.
● Hence, unlike `color{brown}("one-way flow of water")` in `color{violet}("transpiration, food in phloem sap")` can be transported in any required direction so long as there is a source of sugar and a sink able to use, store or remove the sugar.
● `color{violet}("Phloem sap")` is mainly `color{brown}("water and sucrose,")` but other `color{brown}("sugars, hormones")` and `color{brown}("amino acids")` are also transported or `color{brown}("translocated")` through `color{violet}("phloem.")`