EXERCISE 52 



ADVANTAGES FROM DISPERSAL OF SEEDS 

 Materials. Dandelions in seed. 



Directions for work. To appreciate the advantages resulting 

 from dispersal of seeds, study the conditions that would result 

 if seeds were not dispersed. Count the seedlike fruits on a 

 dandelion head or make a close estimate of the number. There 

 is one seed in each fruit. What is the total number of seeds 

 on a head? Estimating on the basis of the number of heads 

 produced by the plant you are examining, as shown by old 

 seed stalks, flower heads, buds, etc., what is the approximate 

 number of seeds produced per dandelion plant ? If these seeds 

 were to fall from the plant without being scattered about by 

 the wind, it may be supposed that they would fall within an 

 area of about one square foot. Supposing them to be evenly 

 distributed throughout this area, how many seeds would there 

 be per square inch ? How many dandelion plants would there 

 be room for in this area providing no other plants occupied 

 it ? How many square inches of the square foot are actually 

 unoccupied by the parent dandelion and other perennial plants ? 

 Do you consider that there would be fair opportunity for 

 any considerable number of new dandelion plants to establish 

 themselves under the conditions supposed above? 



Now watch dandelion seeds when a strong wind is blowing. 

 How can you prove that seeds are carried ? Examine the area 

 within a distance of one or two hundred feet of a patch of 

 dandelions. How much area do you find not occupied by dan- 

 delions ? How much area do you find not occupied by any 

 perennial plants? How many dandelions might find room 

 within the area over which seeds are known to be distributed 

 from the one patch? 



State your opinion regarding the advantage of dispersal as 

 shown by the facts learned in this study. 



References 



BERGEN and CALDWELL. Practical Botany, pp. 146-151. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 166-170. 



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