[Reference- 100% From NCERT XI & XII ]
➡️The wood is actually a secondary xylem.
➡️There are different types of wood on the basis of their composition and time of production.
Imbibition is absorption of water by seeds and dry wood.
➡️The pressure that is produced by the swelling of wood had been used by
prehistoric man to split rocks and boulders.
➡️How would
you describe the swelling of piece of wood when placed in water?
➡️Burning of wood, forest fire and combustion
of organic matter, fossil fuel, volcanic activity are additional sources for
releasing CO2 in the atmosphere
➡️People’s participation has a long history in India. In 1731, the king of
Jodhpur in Rajasthan asked one of his ministers to arrange wood for
constructing a new palace. The minister and workers went to a forest
near a village, inhabited by Bishnois, to cut down trees. The Bishnoi
community is known for its peaceful co-existence with nature. The effort
to cut down trees by the kings was thwarted by the Bishnois. A Bishnoi
woman Amrita Devi showed exemplary courage by hugging a tree and
daring king’s men to cut her first before cutting the tree. The tree mattered
much more to her than her own life. Sadly, the king’s men did not heed to
her pleas, and cut down the tree along with Amrita Devi. Her three
daughters and hundreds of other Bishnois followed her, and thus lost
their lives saving trees.The Government of India has recently instituted the
Amrita Devi Bishnoi Wildlife Protection Award for individuals or
communities from rural areas that have shown extraordinary courage
and dedication in protecting wildlife.
➡️Chipko Movement of Garhwal Himalayas.
In 1974, local women showed enormous bravery in protecting trees from
the axe of contractors by hugging them.
➡️Government of India in 1980s has introduced the concept of
Joint Forest Management (JFM) so as to work closely with the local
communities for protecting and managing forests. In return for their
services to the forest, the communities get benefit of various forest products
(e.g., fruits, gum, rubber, medicine, etc.), and thus the forest can be
conserved in a sustainable manner.
➡️Phycomycetes:
Members of phycomycetes are found in aquatic habitats
and on decaying wood in moist and damp places or as
obligate parasites on plants
➡️Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely
aquatic (both fresh water and marine) organisms. They occur in a
variety of other habitats: moist stones, soils and wood. Some of them
also occur in association with fungi (lichen) and animals (e.g., on sloth
bear).
➡️Spring wood and autumn wood
The activity of cambium is under the control of many physiological and
environmental factors. In temperate regions, the climatic conditions are
not uniform through the year. In the spring season, cambium is very
active and produces a large number of xylary elements having vessels
with wider cavities. The wood formed during this season is called spring
wood or early wood. In winter, the cambium is less active and forms
fewer xylary elements that have narrow vessels, and this wood is called
autumn wood or late wood.
The spring wood is lighter in colour and has a lower density whereas
the autumn wood is darker and has a higher density. The two kinds of
woods that appear as alternate concentric rings, constitute an annual ring.
Annual rings seen in a cut stem give an estimate of the age of the tree.
➡️Heartwood and sapwood
In old trees, the greater part of secondary xylem is dark brown due to
deposition of organic compounds like tannins, resins, oils, gums, aromatic
substances and essential oils in the central or innermost layers of the stem.
These substances make it hard, durable and resistant to the attacks of microorganisms
and insects. This region comprises dead elements with highly
lignified walls and is called heartwood. The heartwood does not conduct
water but it gives mechanical support to the stem. The peripheral region of
the secondary xylem, is lighter in colour and is known as the sapwood. It is
involved in the conduction of water and minerals from root to leaf.
