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Making
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| Making
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| ‹ Secondary Growth › |
| What's the point of secondary growth? |
| As a plant grows, its size requires more support and vascular pathways. The plant is developing a large amount of leaves that need a large amount of water and minerals from the roots. So, in order to do this, the plant creates more xylem to conduct more water. It will also create more phloem to move the carbohydrates from photosynthesis from the leaves to the roots. |
| Each year, the vascular cambium produces a layer of secondary xylem (towards the inside) and a layer of secondary phloem (towards the outside), resulting in an expansion in girth (diameter). The secondary xylem that is produced differs throughout the year (i.e.: spring and summer wood). Spring wood cells are generally thin-walled with a large diameter, compared to summer wood, where the cell walls are thicker and the diameter is smaller. The rings you see when looking at a cross section of a tree is actually secondary xylem. The “line” in-between summer and spring wood is caused by the almost complete lack of growth during the winter. Since a “ring” seems to occur once a year, they can be used to provide an age when counted accurately. Secondary phloem, on the other hand, cannot be used to determine the age of the tree. Secondary phloem, along with the periderm, is what we normally call “bark” on the tree. This “bark” is sloughed off regularly as the tree grows and expands in diameter, or when a mean person rips it off for fun. So, again, you cannot count phloem to determine the age, but you can count xylem to do so. |
| Links: |
| http://koning.ecsu.ctstateu.edu/plant_biology/secondary.html |
| Seed morphology |
| Plumule |
| Made up of two embryonic leaves, which will become the first true leaves of the seedling |
| 1 or 2 Cotyledons |
| Store food that will be used by the embryonic seedling. |
| Monocots produce seeds with one cotyledon (like corn), while dicots produce seeds with two (like peanuts). |
| Hypocotyl |
| Greek for “under”. This is the plant axis BELOW the cotyledons |
| Epicotyl |
| Greek for “over”. This is the plant axis ABOVE the cotyledons. |
| Radicle |
| The embryonic root; will grow into the primary root eventually. |
| Hilium |
| Scar-like feature from where the ovule was once attached to the ovary wall. |
| Seed Coat (sometimes) |
| A “jacket” that protects the seed—that papery stuff that covers a peanut is an example. |
| ‹ Transpiration › |
Transpiration is the evaporation of water from plants. It occurs mainly at the leaves while their stomata are open for the passage of carbon dioxide and oxygen during photosynthesis. |
This process has a good side and a bad side. The good side is that it brings water and minerals up from the roots and into the leaves. It acts as an “engine” to pull these substances up against the force of gravity. However, the bad side is that when the stoma are open, water loss can occur and can dry out the plant. |
updated 3-12-06