Plants 8

Plants 8 - Plants 8 Primary= responsible for extension...

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Plants 8 Primary= responsible for extension growth and for establishing patterns. Lets consider tissues that are formed by meristems other than the shoot/root meristems, therefore they are called secondary. There are cells and tissue types which are secondary which increase the girth of trees. Lets make the cross section of a stem , and follow this stem as it moves from a narrow structure like a twig to a wide trunk of a tree. This cross section is a Eudicot stem showing primary growth. There are 4 vascular bundles each with xylem and phloem. Lets follow these two vascular cell types with time to see what happens to them and see how they are related to secondary growth. If we wait for some time, the phloem is still towards the periphery but the xylem has moved in towards the center. There is a complete layer of phloem and to its inside, a complete layer of xylem. The dots represent places where primary xylem and primary phloem used to be. The thing causing these bundles to separate is by the production of a new meristem. This new meristem extends out from the bundles and makes a complete circle. It also has high cell division activity. It is called the vascular cambium. The cells and tissues formed are secondary. This is what makes a twig have a very wide girth. This new meristem is now producing new cells to its outside and new cells to its inside, both of which are secondary. To its inside it is making new xylem. This is called secondary xylem= Wood. To the outside of the vascular cambium, the new meristem is making new phloem which we call secondary
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Plants 8 - Plants 8 Primary= responsible for extension...

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