Biology Today — December 2017

Epidermis

Cambium

Primary vascular

bundle

Secondary vascular

bundle

Ground tissue

Cortex

Cork

Fig.: T.S. of stem of Dracaena (diagrammatic)

Epidermis

Cambium

Conjunctive tissue

Secondary

vascular

bundles

Vascular bundle

Ground tissue

(primary)

Primary tissue

Secondary tissue

Phloem

Phloem

Xylem

Xylem

Cork cells

Cortex

Fig.: Detailed structure of a part of T.S. of stem of Dracaena

New MCQs

1. The roots do not show distinct annual rings because
   (a) vascular cambium is not active
   (b) roots grow in dark
   (c) secondary xylem is not abundant
   (d) it grows in soil whose conditions remain more or less
   same.


2. Which of the following is not a secondary meristem?
   (a) Interfascicular cambium
   (b) Intrafascicular cambium
   (c) Cork cambium
   (d) None of these


3. In a cross section of dicot root showing secondary growth,
   the primary xylem can be distinguished from secondary xylem
   by which of the following characteristics?
   I. Endarch nature II. Exarch nature
   III. Central in position IV. Broader and thinner vessels
   The primary xylem can be identified by
   (a) III and IV only (b) I and IV only
   (c) II and III only (d) II, III and IV only.
   4. The vascular rays formed in the secondary vascular tissues
   are mainly involved in
   (a) storage of food
   (b) radial diffusion of gases
   (c) conduction of water and organic food
   (d) all of these.
   5. In a section of wood trunk obtained from a tree, the part of
   wood with abundant fibres and high density is referred to
   as
   (a) spring wood (b) autumn wood
   (c) early wood (d) sapwood.
   6. Ring porous wood is considered to be more advanced than
   diffuse porous wood as
   (a) it is composed of 90-95% tracheids
   (b) large sized vessels are present both in spring and
   autumn wood
   (c) broad vessels in spring wood provide better
   translocation
   (d) broad vessels in autumn wood help to fulfill acute
   requirements.