102 



HOW DO SEED PLANTS SUCCEED IN LIFE? 



that plants could grow there. But weeds do grow and flourish 

 under what seem impossible conditions for other plants. Let us 

 see some reasons why. 



Laboratory Exercise. Visit a roadside, vacant lot, or meadow and 

 observe the weeds growing there. Collect and, with the aid of one of 

 the references given at the end of the unit, try to classify the various 

 weeds growing in this area. Take one weed and study it carefully to 

 determine why it is successful in surviving. Estimate the number of 

 seeds produced, ways of scattering seeds, protection of seeds, and other 

 adaptation of the plant to its environment, etc. 



Weeds produce many seeds. One fact readily observed is that 

 many seeds are produced by weeds, be they daisies, dandelions, 

 tumbleweeds, or ragweed. The table that follows shows approx- 

 imately the number of seeds produced by an average sized plant. 

 In your project on weeds, determine as accurately as possible the 

 number of seeds produced by a plant and check the result against 

 this table. 



Seeds Produced by a Sixgle Average-Sized Weed 



Dandelion . . 

 Cocklebur . . 

 Oxeyed daisy . 

 Prickly lettuce 

 Beggar ticks . 

 Tumbleweed . 

 Ragweed . . 



1,700 

 9,700 

 9.750 

 10,000 

 10.500 

 14.000 

 23.000 



Burdock . . 

 Russian thistle 

 Purslane . . 

 Crab grass 

 Willow foxtail 

 Tumble mustard 

 Worm seed 



24,500 



25,000 



69,000 



89,600 



113,600 



1,500,000 



26,000,000 



Individual Project. Make a collection of weed seeds, showing kinds 

 and means of dispersal. 



Weeds have good methods of seed dispersal. We have all 

 seen a dandelion or a thistle and know the feathery parachutes 

 by which their seeds travel. Many of us have spent much time 

 and energy in picking beggar-ticks or burdock burs from our 

 clothes after a scramble through a weed-infested lot. Weed 

 seeds or fruits may have hooks, prickles, fluffy outgrowths, or other 

 appendages, which are used for carriage ; they may roll along the 

 ground as the Russian thistle, or tumbleweed ; or they may have 

 fruit that bursts when ripe, scattering their seeds. Some seeds have 



