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Leaves from one of two species of trees, Aspen (Populus tremuloides) trees and/or from Eastern Cottonwood(Populus deltoides) trees or a bush Common Lilac (Syringa vulgaris) can be collected for this study. The stomatal index on the upper and lower epidermis of each collected leaf will be determined. The number of stomata on a leaf will be determined using clear nail polish, tape, and a glass slide. The number of stomata and epidermal cells will be counted under a microscope on high power (400X). A stomatal index will be determined for the leaf. The Stomatal Index (I) =[S / (E+S)] * 100, where S is the number of stomata per unit area, and E is the number of epidermal cells per same unit area. The data from individual leaves will be combined and a mean will be calculated for each tree sampled. This data will be shared with other study sites and examined for patterns!

  1. Students should be divided into teams of two. 10 leaves from each of 10 trees/bushes should be collected. The leaves from one of the following three species should be collected: Aspen (Populus tremuloides) trees, from Eastern Cottonwood(Populus deltoides) trees, or Common Lilac (Syringa vulgaris). Each tree should be assigned an identifying number (1-10). Data about the species and location of the tree/bush should be recorded on the data form below. This should the exact latitude and longitude of the tree however this location data could be the nearest street address to the tree. Leaves should be collected from the south side of the tree, from approximately shoulder height or higher and from the same position on the twig. Each leaf should be labeled with a tree number and a leaf number on a small piece of masking tape on the distal point of the leaf. Example Tree 1, Leaf 1 would be labeled as T1L1.
  2. Each team of two students should look at two leaves. Each leaf should be painted with clear fingernail polish between the 2nd and 3rd vein. An oval spot approximately one half by one centimeter is sufficient to provide enough leaf surface area to make the counts. This should be done for both the upper and lower surfaces.
  3. Allow the fingernail polish to dry completely.
  4. Firmly press a short strip of clear Scotch tape (not frosted) over the dried nail polish on the lower epidermis. Carefully peel the tape from the leaf and affix it to a clean microscope slide. Place the tape toward one end of the slide perpendicular to the long axis of the slide (cross-wise). Label the slide with a sharpie pen to identify it as being from the lower epidermis of the leaf and the tree number the leaf came from. Example Tree 1, Leaf 1, Lower epidermis would be labeled on the slide as T1L1L. Repeat this procedure for the upper epidermis of the same leaf, placing the tape on the other end of the same slide. This tape would be labeled T1L1U.

  5. Repeat this procedure for each of the collected leaves. Be sure to label each leaf and each slide carefully. Organization of your data is critical.
  6. Trace the leaves on a piece of acetate with 1mm grids mark on it and measure the leaf surface area.
  7. Place the leaves in a plant press. After drying, remove the leaves and store for possible future reference.
  8. Each group of two students should count the stomata and the epidermal cells on the leaf casts of two leaves. Count the stomata on the leaf casts at high power, about 400X although the exact magnification is not important. To successfully count the number of stomata in a field of view you will need to focus, using the fine adjustment, up and down to bring different planes into focus. Both members of the group should count the number of leaf stomata and the number of epidermal cells in the first field of view. They should then compare their counts for the same field of view to insure the accuracy of their count. If there are differences then the two counters should discuss which cells they counted and which ones they did not count. Some stomata and epidermal cells will be partially in or out of the field of view. You can adjust to this by dividing the field of view into imaginary quarter segments. Include in your counts the stomata and epidermal cells touching to edge of the field for the upper right and the lower left quarters. Do not include in your counts the stomata touching the edge of the field in the lower right and upper left quarter. Each group should count 5 randomly selected fields of view per leaf cast and enter the counts on to the data tables.
  9. Complete the data form below with all data, tree species, rainfall this year from January to September 1, and the stomata and epidermal cell counts. Enter Latitude and Longitude for the tree if it is more than one kilometer (.6 mile) from your school site. Enter the stomatal index for the upper surface and the lower surface of the leaf. Calculate the average stomata index for the plant (top index + bottom index) / 2 and record this number for each leaf.
  10. Submit the data, using the electronic form in the data submission area.

School Information:

School Name   
School Number   
Tree Species   
Latitude/Longitude of the tree/bush   
Total Rainfall (January 1 - September 1)   

Stomata/epidermal Cell Counts:

Tree Number: Leaf Number:

Top Counts
Bottom Counts
 
Field 1
Field 2
Field 3
Field 4
Field 5
Field 1
Field 2
Field 3
Field 4
Field 5
Stomatal Pores                              
Epidermal Cells                              
Stomatal Index Top of leaf surface                   Bottom of leaf surface              
[S / (E+S)] * 100      

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