WINTER WEEDS AND SEEDS

PURPOSE:  To identify winter weeds by their common names and perform a germination experiment on weed seeds.

MATERIALS:  Field -- Key to Winter Weeds, small plastic bags with closures, small index cards, pencil.  Lab -- petri dishes, masking tape for labels, filter paper, distilled water.

INTRODUCTION:  Winter weeds are the dead remnants of last year's green plants.  They are commonly seen in open fields and along roadsides.  You probably know the names of many of them when you see them in flower during the summer and autumn.  If you look closely at them in winter, you may still be able to find seeds.  Most of the seeds will be carried to other places by wind or animals.  If they land in a suitable place they may germinate and produce new plants in the spring.

In this activity, you will go outside to identify some of the many different kinds of winter weeds.  You will also collect their seeds, which vary in size and number.  Then you will do an experiment to determine if the rate of germination is related to seed size.

PREDICTION:

1.  Do you think the size of seeds has any effect on germination rate?    Explain your ideas.

FIELD PROCEDURE:

A.  Go to an open field that has many weeds standing up through the snow.

B.  Using the Key to Winter Weeds, identify as many weeds as you can by their common name.

C.  Look for seeds on each kind of weed you identify. Some plants will have no seeds.  Collect seeds from the plants that have them using the following method:

(1) Put at least 25 seeds of the same species in a plastic bag.

(2) Write the name of the plant on an index card.  Record how you think the seeds are dispersed (wing or animals).  Estimate how abundant the plant is in your study area (common or rare). 

(3) Put the index card in the bag and seal it.

LAB PROCEDURE:

D.  Prepare one petri dish for each seed sample you collected using the following method:

(1) Label the cover of the dish with the name of the plant.

(2) Place two pieces of filter paper on the bottom of the dish.  Moisten the paper with distilled water.  A thin film of water should cover the bottom of the dish.

(3) Count out 25 seeds from the plastic bag onto the moistened filter paper.

E.  Using information from the index cards, record on your data table the names of the plants you are testing.  Record the abundance (common or rare) of each plant in your study area.  Describe the distinctive features of the seeds, the possible dispersal method, and the seed size.

F.  Stack the petri dishes and store them in a convenient place, out of direct sunlight and at room temperature.  Keep the filter paper moist.  In a few days the seeds will begin to show signs of germination -- a tiny "root" called the hypocotyl will appear.

G.  After one week count and record the number of seeds that have germinated in each petri dish.

H.  Calculate the germination rate for each plant using this formula:  % Germination = Number of Germinated Seeds X 100

Total Number of Seeds

I.  Share your data with others in your class.

J.  Construct a bar graph with % germination on the vertical axis, and individual species on the horizontal axis.

DATA TABLE:

Plant Name

Abundance (Rare or Common)

Distinctive Features of the seeds and Dispersal Method

Seed Size (Large or Small)

Germination # seeds

Germination %

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CONCLUSIONS:

2. Which species of winter weeds were most common in your study area?

3. Which seeds had fluffy parachutes attached?  What is their function?

4. Which seeds had hooks or barbs?  What is their function?

5. Which species had the largest seeds?  Which had the smallest seeds?

6. Which species showed the highest seed germination rate?  Which species had the lowest germination rate?

7. Does the size of the seed affect the rate of germination?  Was your prediction correct?

DISCUSSION:

8. What conditions are necessary for seed germination?

9. Why do you suppose that some of the seeds did not germinate?

10. Are the plants with the highest seed germination rate common or rare in your study area?  Use examples from class data to explain your answers.

11. What factors, other than seed germination rate, could account for the abundance and distribution of weed plants?