Extra Information

*XYLEM*

-carries water from the roots upward
-early xylem were trachieds with tapered ends, pits where water flows through
-eventually, open-ended vessel elements evolved in plants
-have a strong wall to contain water pressure

*PHLOEM*

-carry liquid sugars from leaves downwards
-sieve tubes carry the sugars
-companion cells provide cell functions (sieve tubes lose their nuclei)

Algae is the proposed ancestor of plants.

Evidence of this is: 

-similar molecular pigments
-both produce starch
-cell walls are cellulose
-similar DNA sequences
-similar life cycles

-Mosses are early land plants
-Water is absorbed externally
-There is no vascular system
-Later, plants evolved stems (in competition for sunlight)
-Water and nutrient transport required vascular tissue

Water is needed for reproduction and is also needed inside the cell.

Our lab procedure:

Some information:

Xylem are vascular cells that are stained so that their thick walls tend red (although sometimes other cells stain red, such as the epidermis).  They are usually larger than phloem vascular cells, which have thinner walls and are not stained.  Remember that you are looking at a cross section of long tubes that begin in the roots and extend to the leaves.  In the vascular bundles in the leaves, the xylem tend to be located on the upper side of the leaf, while the phloem tend to be on the lower side.  In the roots and stems the xylem tend to be found towards the center while phloem are found towards the outside.  Starch turns purple under iodine stain which was what we used in this lab.