Spring wood , autumn wood, sapwood, heartwood - Annual ring

• In tropical area, the growth of secondary xylem is continuous and in others, the growth is quite distinct and appears in form of annual ring. 

• There are favourable or unfavourable season for the plants. 

• In temperate areas, spring and early summer are favourable whereas autumn and winter are unfavourable season.

Autumn and Winter wood - 

• During spring and early summer, a large amount of secondary wood is formed due to rapid divison of vascular cambium. It is called spring wood. 

• Spring wood has large and light staining xylem elements.

• During unfavourable season, the activity of  vascular cambium decrease and perform few cell divison during autumn. This wood is called autumn wood or late wood. 

• The autumn wood is made up of smaller and dark  xylem elements. 

• This wood also contain more tracheids and vessels. Autumn wood is much darker and has large density than spring wood. 

Remember 👌👌 After autumn wood and before spring wood , there is no growth . 

• Light spring wood and dark autumn wood form an annual ring or growth ring . It represents the total formed secondary xylem in year. 

• By counting the number of annual ring, the age of tree can be calculated with the help of apparatus called increment borer. 

Sap wood and Heart wood - 

• In older stem, the wood or secondary xylem is  differentiated into sap wood and heart wood.

• Sap wood or alburnum is outer light coloured functional wood. 

• Sap wood contain living cell and participated in conduction of sap. 

• Heart wood or duramen is has central or  dark  coloured non functional wood where living cell are degenerated and treachery elements are plugged.  

• Duramen is formed through the activity of xylem parenchyma cells. The intrusion of parenchyma cells into treachery element are called tyloses. 

• The parenchyma cells are finally lignified and dead. The various biochemical product are deposited called extractive. 

• These extractive include tannins, resins gums,  oils, aromatic substances and essential oils. They are antiseptic and coloured. 

• Heart wood is dark brown and not damaged by microorganism and insect. 

• This wood is heavy, stronger, and more durable but it is prominently attached by fungi.