2. Based on the appearance of these plants and what you know about vascular tissue, determine where vascular tissue evolved on phylogeny 1. Remember “the rule of thumb” (if you’re not sure what this is, ask your TA). Where did this trait evolve?

3. On the poster at the station, there are pictures of four vascular plants – Psilotum, a fern, a pine, and a Eucalyptus tree (be sure to note the scale bars in each image). Based on the sizes of the various plants and their position on the phylogeny, what did the bifacial vascular cambium (BVC) allow plants to do? What advantages do plants that possess this type of tissue have over those that do not?

4a. What two tissues are present in each vascular bundle?

4b. What does each tissue do?

4c. The active growth region, where new cells are produced by the division of existing cells, is the vascular cambium. As new cells are produced, what happens to the existing cells in each bundle?

4d. Plants with secondary growth produce different quantities and diameters of xylem cells during different times of the year. In the spring, when water is plentiful, would you expect plants to produce more or less new xylem cells; would you expect these cells to be smaller or larger in diameter? How about in the summertime when water is scarce?

4e. Based on your answers to 4c and 4d, what are tree rings, and how do they form?

Examine the cross-section of a tree shown below and label the location of springwood, summerwood, the BVC, the xylem, and the phloem. The BVC has been done for you.

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4f. Which labels go with the four blanks? Your options are xylem, phloem, springwood, and summerwood.

5a. Examine the images above the large phylogeny – zoom in so that you can see the stem cross-sections for each plant. You should notice that there is one clade that has scattered vascular bundles – these are the monocots. Which clade (A-D) is the monocots?

5b. Based on the phylogeny, are the scattered vascular bundles of monocots (i.e. the absence of a bifacial vascular cambium) an ancestral or derived state in angiosperms? Why?