Secondary Growth Flashcards
Define secondary growth
Increase in the diameter of stems and roots in plants due to the new cells produced by lateral meristems is called secondary growth
What are the plants that undergoes secondary growth
Woody perennial plants including all gymnosperms species and many dicot species
What is the meristem that is involved in secondary growth
Lateral meristems
What are the two types of lateral meristems that produces new cells for secondary growth
Vascular cambium and cork cambium
What is the function of vascular cambium in secondary growth
Produces secondary xylem towards primary xylem and secondary phloem towards primary phloem increasing vascular flow and support for the shoot
What is wood
Secondary xylem
What type of cells are found in the tough thick covering produced by the cork cambium
Wax impregnated cells
What is the function of the wax impregnated cells produced by the cork cambium
Protect the stem from water loss
Protect the stem from invasion of insects bacteria and fungi
When does the second every growth of woody plants occur in relation to primary growth
Simultaneously
How is the secondary vascular tissue produced
By the action of vascular cambium
Describe the presence of the vascular cambium in a typical woody stem
The vascular cambium consists of a continuous cylinder of undifferentiated cells of often only a single cell layer in thickness located outside the pith and the primary xylem and to the inside of cortex and primary phloem
Where does the vascular cambium add the secondary xylem and secondary phloem
Secondary xylem to the inside of the cambium secondary phloem to the outside
How does the vascular cambium appear in a cross section
As a ring of initials
How are the long initials oriented
They are oriented with their long axis parallels the axis of stem or root
What is the function of long initials
They produce cells such as
Tracheids, vessel elements, fibres and parenchyma of xylem
Sieve tube elements, companion cells, phloem fibres and phloem parenchyma
How are the short initials oriented
Perpendicular to the axis of the stem or root
What is the function of short initials
Produce vascular rays
What are vascular rays
Mostly parenchyma cells that connect secondary xylem and phloem
What are the functions of vascular rays
Connect secondary xylem and phloem
Store carbohydrates
Aid in wound repairing
What accounts for the hardness and strength of wood
The walls of secondary xylem cells being heavily lignified
What happens to the epidermis during the early stages of secondary growth
The epidermis is pushhed outwards causing it to split dry and fall off
What phones the cork cambium
A cylinder of dividing cells that arise in the outer layer of co tax in stems and in the pericycle in the roots become meristematic forming a cork cambium.
To which directions do the cork cambium produce new cells
Both interior and exterior
What happens to the cells that are formed to the exterior of cork cambium
They become cork
What is known as periderm
Cork cambium and the tissues it produces
How do cork cells become dead cells when they mature
As they mature they deposit a vaccine hydrophobic material called suverine in the walls
What is the function of cork tissues
Act as a barrier that helps protect the stem or root from
water loss
physical damages and
pathogens
True or false
Periderm is impermeable to water and gases
True
What is the adaptation periderm have for gas exchange
Small pose known as lenticels are present
How are the lenticels formed
By loosely arranged cork self
Appearance of lenticels
Horizontal slits
What are the small pores present in the periderm for gaseous exchange called?
Lenticels
Lenticels are formed by loosely arranged cork horizontal slits.
What happens to the cork cambium as the stem or root grows?
It breaks and loses its meristematic activity, becoming cork cells
These cork cells together form the periderm.
What is initiated inside the cork layer after the original cork cambium is broken?
A new cork cambium
This new cork cambium will produce a new layer of cork.
What occurs as new cells are added to the cork?
The outer regions of cork crack and peel off
This process is common in many tree trunks.
What contributes to the increase in girth of the stem or root during secondary growth?
Tissue layers produced by vascular cambium and cork cambium
This process is essential for the overall growth of the plant.
What is commonly and incorrectly referred to as bark?
Cork
The main components of bark are secondary phloem and periderm.
What are the main components of bark?
- Secondary phloem
- Periderm
Bark includes all tissues outside of the vascular cambium.
True or False: The epidermis is a main component of bark.
False
Bark consists of secondary phloem and periderm, not the epidermis.
