There are many tissues prodeced outside the vascular cambium in the stem . Explain them .

Explanation

(i) Bark : The term 'bark ' is commonly applied to all the tissue outside the vascular cambium of stem (i.e., periderm,cortex,primary phloem and secondary phloem).
(ii) Bark protects the plant from parasitic fungi and insects, prevents water loss by evaporation and guards against variations of external temperature.
(iii) It is an insect repellent, decay proof, fire proof and is used in obtaining drugs or spices.
(iv) The phloem cells of the bark are involved in conduction of food while secondary cortical cells involved in storage.
(v) if the phellogen forms a complete cylinder around the stem , it gives rise to ring barks.
Example : Quercus .
(vi) When the bark is formed in overlapping scale like layers, it is known as scale bark.
Example: Guava. While ring barks normally do not peeled off, scale barks peeled off.
Lenticel :
(i) Lenticel is raised opening or pore on the epidermis or bark of stems and roots .
(ii) It is formed during secondary growth in stems
(iii) When phellogen is more active in the region of lenticles, a mass of loosely arranged thin-walled parenchyma cells are formed .
(iv) it is called complementary tissue of or filling tissue.
(v) Lenticel is helpful in exchage of gases and transpiration called lenticular transpiration.