Tag: secondary growth in stem

Tectona grandis - Hard wood is present.

The large sized, slightly raised sports or aerating pores present in the cork tissue or are called Lenticels. These are the patches on the surface of the bark. These are found in old dicotyledonous stems. These are formed in the place of stomata. They have outer raised margins and internally, loosely arranged colourless parenchyma cells are present, called as complementary cells, These are meant for gaseous exchange.

Secondary xylem without vessels is called non-porous wood. It is found in the wood of gymnosperms. 

In dicotyledonous stems, during intra stellar secondary growth, a ring of cambium called vascular cambium is formed.  In the plants growing temperate regions, the activity of vascular cambium is influenced by the existence of maximum seasonal variations. In the spring or early summer, due to the existence of favourable conditions, a large amount of secondary xylem is formed. it is called Springwood or early wood. It is lighter in colour with low density. In the autumn season, due to the presence of unfavourable conditions, less amount of wood is formed. it is called autumn wood or latewood. It is darker in colour with higher density.

So the correct option is ‘Spring wood and autumn wood’.

In Quercus and Pinus, during secondary growth, secondary xylem show vessels without pores, also non porous vessels. It is loose and soft. So it is not considered as heart wood. So, heart wood is absent in Quercus and Pinus.

So, the correct option is ‘Quercus and Pinus’.

A.Salix  - wood is used in making boxes, brooms, cricket bats, Hockey bats,cradle boards, chairmans and other furniture, dolls, flutes, poles, sweat lodges, toys, turnery, tool handles, veneer, wands and whistles.

B.Morus – wood is used in making Fence posts, furniture, and turned objects

C.Picea – wood is used in buildings

d.Phytelephas – wood is used in making ivory.

So, the correct option is ‘ Salix’.    

In Dalbergia, during secondary growth, hart wood is formed. It consists of vessels, trachieds and parenchyma in equal proportions.

So, the correct option is ‘Vessels, trachieds, and parenchyma in equal proportions’.

In the trunk and older branches of the large trees, only the outer secondary xylem i.e. sapwood serves in water conduction. Whereas the inner part i.e. heartwood,  is composed of dead but structurally strong primary xylem. Thus the youngest layer of secondary xylem is located just inner to sapwood and not in the centre of the stem.

The correct answer is option C.

• Wood specific gravity is the measurement of the amount of dry cell-wall material per unit volume of the wood. 
• It is in such a way that probably the single most important predictor of the properties of wood. 
• It is among the species as woods range in specific gravity from less than 0.05 for Aeschynomene hispida Wild.
• Thus, the correct answer is option D.

• The hardness of a cell refers to the sturdiness of the cell wall because of the presence of lignin and cellulose present in them.
  
• Lignin is a naturally occurring complex organic cross-linked phenolic polymer that forms an important structural material of the plant cell wall (secondary cell wall).
• They are mainly found regions of wood and bark as they provide rigidity and prevents deterioration.
  
• It also provides support to tissues of vascular plants and few algae.
• So, the correct answer is 'Lignin'.