Question

what is meant destarching why do plants get destarching when kept im cotaining darkness about 48 hourly

Answer 1

destarching means removing excess starch from plants.
destarching is done by keeping the plant in darkness so it cannot prepare food due to lack of light and use up its stored food(starch). this using up takes about 48 hrs.
hope it helps

Answer 2

Destarching occurs when part of a plant is "deprived of starch, as by translocation". It is also the process of eliminating starch reserves in a plant for experiments concerning photosynthesis. This is done by leaving the plant(s) in a dark place for a long period of time.