FRUITS 



61 



sule, splits along the edge of each locule, snaps back, and throws 

 the seed for some distance. Jewel weed fruits burst open in some- 

 what the same manner. Make 

 observations on jewel weed to 

 find out if possible how the ex- 

 plosion of the fruit is caused. 



Large Numbers of Seeds. — ■ 

 Plants which do not have espe- 

 cial means for scattering their 

 seeds may make up for this by 

 producing a large number of 

 seeds and holding them in pod- 

 like fruits which are easily 

 shaken by the wind. The poppy 

 and jimson weed are familiar 

 examples of such plants. Each 

 capsule of jimson weed contains 

 from four hundred to six hun- 

 dred seeds, depending upon its 

 size. If all of these seeds de- 

 veloped, the whole earth would 

 soon be covered with jimson weed, to the exclusion of all other 

 forms of plant life. That this is not the case is due to the fact 

 that only those seeds which are advantageously placed can de- 

 velop; the others will, for various reasons (lack of moisture to 

 start the young seed on its way, poor soil, lack of air or sunlight, 

 overcrowding), fail to germinate. 



The Struggle for Existence. — Those plants which provide best 

 for their young are usually the most successful in life's race. 

 Plants which combine with the ability to scatter many seeds over 

 a wide territory, the additional characteristics of rapid growth, 

 resistance to dangers of extreme cold or heat, attacks of parasitic 

 enemies, inedibility, and peculiar adaptations to cross-pollination 

 or self-pollination, are usually spoken of as weeds. They flourish 

 in the sterile soil of the roadside and in the fertile soil of the 

 garden. By means of rapid growth they kill other plants of 

 slower growth by usurping their territory. Slow-growing plants 



Wild geranium (crane's bill), showing method 

 of seed dispersal; a, flower with seeds 

 nearly ripe; b, flower with seeds ripe; 

 c, flower after having thrown seeds. (After 

 Lubbock.) 



