430 PLANTS AND THEIR RELATION TO MAN 



FlG. 295. The silky hairs act as sails for 

 the milkweed seeds. 



seed which falls to the 

 ground under good con- 

 ditions develops into a 

 plant and thus keeps 

 on the earth the type 

 of plant from which it 

 came. 



Some plants growonly 

 from seeds and would 

 disappear from the earth 

 if they failed to produce 

 seeds for future plants. 

 Other plants, like the 

 iris and wild ginger, are 

 not entirely dependent upon seeds for future growth because 

 they possess a hardy rootstock which survives the winter and 

 sends up new shoots in the spring. Still other plants, like the 

 lily, hyacinth, and onion, produce bulbs which remain alive 

 after the rest of the plant 

 has died, and which de- 

 velop into flourishing 

 plants the following sea- 

 son (Fig. 297). 



The survival of the 

 fittest. Seeds do not all 

 develop into mature 

 plants. The milkweed 

 seeds, for example, which are carried far and wide by the wind 

 do not all become mature plants. Some of them settle in barren 

 places where their roots cannot get a foothold ; or drift into 

 ponds and streams where they die ; or fall among stronger 

 plants which choke them and crowd them out. Some seeds 

 are eaten by birds, squirrels, and other animals, and some are 



FIG. 296. A, cocklebur; B, burdock. 



