Biology Times (^19)
March
the impervious nature of cork cells to air, narrow slightly raised pores are formed in the place of stomata.
These are known as lenticels.
They are formed due to the activity of cork
cambium. At first the parenchyma cells adjoining
the sub-stomatal cavity divide in different planes
and form a group of stationary cells. After this
the cork cambium produces loosely arranged
parenchyma cells towards the periphery of the
stem. All these cells are known as complementary
cells. As the number of these cell increases, the
epidermis gives way and the complementary
cells form raised aperature. In a cross section of
a lenticel, the opening lead to loosely arranged
complementary tissue and the phellogen is seen
underneath this tissue.
In between the complementary cells, intercellular
spaces are present, through which air reaches the
inner tissues and carbondioxide along with water
vapour comes out.
The cork (phellum), cork cambium (phellogen)
and secondary cortex (phelloderm) together
constitute the periderm.
In a transverse section of one or two year old
woody stems two zones – bark and wood are
clearly visible. The entire zone outside the
vascular cambium is known as bark. It includes
periderm, pericycle, primary cortex, primary and
secondary phloem.
The bark and cork of some plants are
commercially important. The bark of cinchona is
used for the extraction of quinine, which is the
natural medicine against malaria. The dried bark
of cinnamom is used as spice. The cork of bottle
cork (Quercus suber) is used as commercial cork.
- Primary vascular bundles are produced by the
a. Procambium b. Intercalary meristem
c. Protoderm d. Lateral meristem
- Primary growth in plants is initiated by the
a. Apical meristem b. Lateral meristem
c. Vascular cambium d. Dermal tissue - Tyloses are
a. Laticiferous channels
b. balloon like projections
c. Secretory cells
d. Lenticels - Other names of secondary cortex, cork cambium
and cork are
a. Phellum, Phelloderm & Phellogen
b. Phellogen, Phellum & Phelloderm
c. Phelloderm, Phellogen & Phellum
d. Phellogen, Phelloderm & Phelllum - Secondary growth is absent in
a. Dicot stem b. Monocot root
c. Monocot stem d. Dicot root - Cork cambium is a