Secondary growth

Cork

The outermost layer is produced by the cork cambium. It is water repellent due to suberin

Lateral meristem

It is where the growth or girth is happening. For secondary growth this is called the cambium. There is a cork cambium and a vascular cambium.

Cork cambium

• Produces water repellent cells of cork.

• It is the outside layer of a tree

• Everything it produces to the outside is called suberin which has properties keeping water from getting into the plant, it prevents mechanical + insect injuries. 

• It can also produce phelloderm on the Inside  -> phelloderm is made out of parenchyma cells.

Phelloderm

Parenchyma cells made to the inside of the cork cambium. 

Suberin

Has properties that keep water from getting into the plant preventing injury (mechanical + insecticidal)

Vascular cambium

Region of cell growth that leads to phlegm and xylem.

Cell division to the outside = phloem

Cell division to the inside = xylem

Turgor

Water used to increase the internal soils pressure from within a cell. This is used to expand cells during cell differentiation of xylem and phloem in the vascular cambium. 

vascular rays

Are made of parenchyma cells they help transport nutrients and water between xylem and the cortex

Cytorrhysis

the complete and irreversible collapse of cell walls under extreme desiccation.

Carbon starvation

An inability to carry out metabolic, defense, or hydraulic functions due to a lack of stored carbohydrates

Cohesion-tension theory

Movement through xylem is through 2 forces that lead to the transpiration of water.

Cohesion

When water molecules stick together (though H-bonds) form a column of cells all bound together.

Tension

It comes from the loss of water (transpiration) through stomata creating a negative pressure when it exerts a pole on the whole column.

Traechids

Cells that are  connected to each other with bordered by pits, the water moves from one cell to another. These are simpler structures. They are dead at maturity.

Vessel members

Are connected by perforation plates + bordered pits. They are stacked together to create a vessel. Dead at maturity. They make up vessels which are usually longer and wider than traechids. Not found in gymnosperms

Structural fibers

Living at maturity and made of sclerenchyma cells help to give the wood more structure. 

Not found in gymnosperms.

Pits

Found cell to cell they are for protection and prevention. 

Hagen-Poiseuille equaiton

Formula for the laminar flow through a long cylindrical pipe. Explains why larger vessels will conduct more water. This is only for water flow it does not take into account perforation plates or pits.

Embolism

 water columns will break under very negative pressure

Air seeding

when there are air bubbles in the xylem. If a branch is cut off then some air may be able to enter the xylem. The air bubble can then move around the xylem. This is more common in dehydrated plants. The bubble goes from vessel to vessel via bordered pits, and is dependent on the size of the pits.

Freeze-thaw

 it occurs over winter and early spring during freezing. During the freeze any gas discovered in a solution that doesn't stay dissolved when the water freezes can create an air bubble. During the thaw the air bubbles expand

Sapwood

It is water conducting wood. It is active wood. It is made out of water-conducting xylem and living parenchyma cells.

Heartwood

It is fully dead wood, it cannot conduct water and serves as support. It naturally accumulates “extractives” like resin to deter against pests like fungi and insects. It is usually darker in colour and can sometimes be completely rotted out.

Extractives

Resin, tannins and lignins

Tyloses

Can be in response to pathogen infection in the wood. It is where the parenchyma cells make outgrowths into vessels to stop water flow.

Ring porous

Type of tree ring where there is a clean separation between early wood and late wood. Where early wood/spring wood has longer and wider vessels. And later wood/summer wood has smaller vessels or is all fibres and traechids. 

• ++Ecologically they will leaf out later in the spring because they rely less on xylem from previous seasons. This is because the big vessels containing more water will inevitably experience more freeze-thaw cavitations/embolisms. They then lose a lot of their conductivity every winter. This means come spring they cannot just make leaves at the same time they start making wood. 

• Ex, Oak, elm, ash

Early wood

Also known as spring wood. It is more conductive and has large vessels. L

Late wood

Also known as summer wood. IT has smaller vessels or just traecheids and fibres. It has lower conductivity.

Diffuse porous

• There is no distinction between early and late wood. The distribution of early and late wood seems random or has odd patterns. 

• This makes the rings hard to distinguish and the years hard to count. 

• Ex, aspen, maple.

• ++Ecologically they will leaf out earlier because they have xylem that is ready to go in the spring. They will generally have less heartwood

Gymnosperms

Also known as softwood. The rings are ~uniform in size due to the tracheids. They can get a little smaller at the end. The Big circles found are resin ducts. Because they do not have sclerenchyma fibers there is a lower risk of embolism. Most cells remain functional, the switch is w/ natural cell death

Resin ducts

Often embedded in the xylem or other tissues, they conduct different metabolites, often sticky ones, they protect the plant after injuries or detect insects, etc..

Laticifers

A latex producing cell found in the cortex or phloem, is used for healing wounds and protects it from insects. Only found in certain species. Ex, rubber tree.