Soft Wood Generally, the gymnosperm wood, which lacks vessels is known as non- porous wood or soft wood . Example: Pinus . Figure . : Structure of porous (a) and non-porous wood (b) Differences between Porous Wood and Non-porous Wood Porous wood or Hard wood, Example: Morus Non porous wood or Soft wood, Example: Pinus Common in angiosperms Common in gymnosperms Porous because it contains vessels Non-porous because it does not contain vessels a b Activity of Vascular Cambium The vascular cambial ring, when active, cuts off new cells both towards the inner and outer side.
The cells which are produced outward form secondary phloem and inward secondary xylem. a b c d e f Cambium First formed xylem Second formed xylem First formed xylem Cambium Third formed xylem First formed xylem Second formed xylem First formed phloem Cambium Second formed xylem Third formed xylem First formed xylem First formed phloem Cambium Second formed xylem Third formed xylem First formed xylem Second formed phloem Fourth formed xylem Cambium A Portion of cambium Figure . : Diagrammatic representation of vascular cambial activity (a–f) At places, cambium forms some narrow horizontal bands of parenchyma which passes through secondary phloem and xylem. These are the rays.
Due to the continued formation of secondary xylem and phloem through vascular cambial activity, both the primary xylem and phloem get gradually crushed. Secondary Xylem The secondary xylem, also called wood , is formed by a relatively complex meristem, the vascular cambium, consisting of vertically (axial) elongated fusiform initials and horizontally (radially) elongated ray initials. Complementary cells Cork cambium (Phellogen) (Periderm) Cork (phellem) Secondary cortex (Phelloderm) Collenchyma Parenchyma Secondary phloem Cambium Autumn wood (secondary xylem) Spring wood (secondary xylem) Secondary medullary ray Primary xylem Pith Lenticel Epidermis Figure . : Secondary growth in two year old dicot stem – A portion enlarged Fascicular cambium Pith a b Secondary Phloem Vascular cambial ring Secondary xylem Phellem (Cork) c d Epidermis Cortex Bundle cap Primary Phloem Primary Xylem Inter fascicular cambium Phellogen (Cork cambium) Phelloderm (Secondary cortex) Medullary ray Figure .
: Secondary growth in dicot stem