from the phellogen as a part of the periderm of stems and roots in seed plants. Differences Between Phellem and Phelloderm Phellem (Cork) Phelloderm (Secondary cortex) It is formed on the outer side of phellogen. It is formed on the inner side of phellogen. Cells are compactly arranged in regular tires and rows without intercellular spaces.
Cells are loosely arranged with intercellular spaces. Protective in function. As it contains chloroplast, it synthesises and stores food. Consists of non- living cells with suberized walls.
Consists of living cells, parenchymatous in nature and does not have suberin. Lenticels are present. Lenticels are absent. Figure .
: Guava tree showing scale bark Figure . : Quercus Tree-showing ring bark Lenticel Lenticel is raised opening or pore on the epidermis or bark of stems and roots. It is formed during secondary growth in stems. When phellogen is more active in the region of lenticels, a mass of loosely arranged thin-walled parenchyma cells are formed.
It is called complementary tissue or filling tissue . Lenticel is helpful in exchange of gases and transpiration called lenticular transpiration . Lenticel Complementary cell Phellogen (Cork cambium) Phelloderm (Secondary cortex) Epidermis Phellem(Cork) Figure . : Structure of Lenticel .
Secondary Growth in Dicot root Cambial ring Pericycle a b c d e Epidermis Phellogen (Cork cambium) Primary phloem Secondary phloem Phloem ray Cambial ring Primary xylem Secondary xylem Xylem ray Epidermis Cortex Endodermis Pericycle Primary phloem Secondary phloem Primary xylem Secondary xylem Primary xylem Cambium Primary phloem Pericycle Endodermis Epidermis Figure . : Different stages of the secondary growth (diagrammatic) in a typical dicot root (a–e) Secondary growth in dicot roots is essential to provide strength to the growing aerial parts of the plants. It is similar to that of the secondary growth in dicot stem. However, there is marked difference in the manner of the formation of vascular cambium.
The vascular cambium is completely secondary in origin. It originates from a combination of conjunctive tissue located just below the phloem bundles, and as a portion of pericycle tissue present above the protoxylem to form a complete