Definitions / Explanation :
$(i)$ Early wood
$(ii)$ Late wood
$(i)$ In the spring season, cambium is very active and produces a large number of xylary elements. This wood is known as spring wood or early wood.
$(ii)$ In winter, cambium is less active and forms fewer xylary elements. It is called late wood or autumn wood.
In the primary tissues of the stem, the cambium separating xylem and phloem is called
Secondary growth or increase in diameter is due to
$A$ : Oldest layer of sapwood lies just outside vascular cambium.
$R$ : Sapwood contains actively conducting vessels and occupies central part of stem.
The functional xylem of dicot tree is